027 / 75 · Savory surprises to pass
Squash Polenta Diamonds with Mustard Mushrooms
24 polenta triangles arranged as 12 diamond-shaped pairs, with mushroom topping; 2 triangles per buffet portion · Active 50 min · Cook 1 hr 15 min · Total 4 hr 10 min (chill-set preparation and hot finish)
Cold-travel planning: 3 hr 40 min; follow the stated cooling endpoint and finishing route.
Print recipe · PDFThe diamonds are made from two triangles, so every cut piece belongs on the platter. Roasted squash gives the polenta a warm color and soft sweetness; mustard mushrooms provide the darker, savory spoonful on top. Chill the slab properly before cutting, and the finishing bake becomes straightforward.
A slab needs a real cooling interval
Fresh polenta behaves like porridge, not a cracker. Spread it evenly while hot, then let refrigeration do the work before you ask it to hold a shape. A shallow metal pan cools more efficiently than a thick ceramic dish and gives a useful straight edge for cutting. The recipe does not depend on a specialist diamond cutter: make twelve rectangles and halve each diagonally. The paired triangles suggest a diamond on the plate without leaving a collection of wasted corners.
Keep the mushrooms concentrated
Mushrooms are the only topping, so their water matters. Give them a wide hot pan and wait for the released liquid to disappear before adding mustard. The final mixture should sit on a spoon rather than run over the polenta. Carry the topping separately if the journey is long; dry edges stay more appealing than a platter assembled hours ahead. This is a fork-sized buffet portion, not a fragile one-bite canapé, and a small plate makes it easier to enjoy.
Ingredients
- 14 oz (400 g) peeled butternut squash, cut into ¾ in/2 cm dice
- 2 tbsp (30 ml/28 g) olive oil, divided: 1 tbsp for squash and 1 tbsp for brushing polenta
- 2¾ cups plus 2 tbsp plus 2 tsp (700 ml) low-sodium vegetable stock
- 1¼ cups (300 ml) milk
- 1¼ cups (200 g) quick-cooking polenta, a product specifying about 5 parts liquid to 1 part polenta by weight
- ¾ tsp (4.5 g) fine salt, divided: ½ tsp in polenta and ¼ tsp in mushrooms
- 1¼ lb (600 g) mushrooms, finely chopped
- 1 tbsp (15 g) unsalted butter
- 2 tbsp (30 g) Dijon mustard
- ¼ tsp (0.5 g) ground black pepper
Set out
Oven, Shallow 9×13 in (23×33 cm) metal pan, at least 1½ in/4 cm deep, Parchment paper, Large saucepan, Potato masher, Whisk, Wide skillet, Knife, Food thermometer, Shallow containers and cooler with ice packs, Two large rimmed baking sheets, each at least 15×11 in/38×28 cm, cleaned and relined for the finishing bake
Allergens
Milk, Mustard. Check labels and substitutions.
Make it
- Heat the oven to 425°F (220°C). Toss the squash with 1 tbsp of the oil on the first sheet. Roast 25–35 minutes until soft, turning once. Mash thoroughly. Line the shallow pan with parchment, leaving two lifting handles.
- Bring the stock and milk to a simmer in the saucepan. Whisk in the polenta and ½ tsp salt; cook for the product’s full quick-cooking time, usually 5–8 minutes, stirring to prevent catching. Stir in all the mashed squash. The mixture should be thick enough that the spoon leaves a track. Spread into the lined pan in an even layer about ¾ in/2 cm thick.
- Let steam escape for 15 minutes, then refrigerate the shallow pan uncovered until cool, covering once cold. Allow at least 2 hours in the refrigerator, until firm and at 40°F (4°C) or below. Do not leave the slab on the counter to set. For cold transport, cook the mushrooms using step 5 while the slab chills, then refrigerate them in a separate shallow container for about 60–90 minutes, and longer until at 40°F (4°C) or below. This overlaps the slab’s 2-hour cold-set. Cut and pack only after both components are fully cold.
- Heat the oven to 425°F (220°C). Lift out the slab. Cut into 12 rectangles in a 3-by-4 grid, then cut each rectangle diagonally to make 24 triangles. Divide between the two clean lined sheets with about 1 in/2.5 cm between pieces, brush with the remaining 1 tbsp oil and bake 22–28 minutes, turning the triangles and swapping sheet positions halfway, until the surfaces are dry and the centers reach 165°F (74°C).
- While the triangles bake, melt the butter in the wide skillet. Add the mushrooms and cook over medium-high heat 10–14 minutes, stirring, until tender and their water has evaporated. Stir in mustard, the remaining ¼ tsp salt and pepper for 1 minute. Pair two hot triangles into each diamond-shaped portion and divide all the mushrooms among the 12 pairs. Serve promptly. If the mushrooms were cooked and chilled for transport, reheat them to 165°F (74°C) instead of serving them lukewarm; keep at least 140°F (60°C) if briefly holding.
Bring it
Transport firm chilled triangles and chilled mushroom topping in separate shallow containers in a cooler at 40°F (4°C) or below. Pack both finishing sheets and the serving spoon. During packing, travel and display, keep cold food at 40°F (4°C) or below and hot food at 140°F (60°C) or above. Allow no more than 2 hours combined outside those controls, or 1 hour above 90°F (32°C). Discard food beyond that limit.
Finish at the gathering
Reserve an oven with space for both finishing sheets for 25–30 minutes at 425°F (220°C) and a skillet or microwave-safe bowl for reheating the mushrooms to 165°F (74°C). Brush and bake the triangles as in step 4. If the host cannot supply this equipment, finish at home and bring only with a carrier verified to maintain at least 140°F (60°C). Do not rely on residual warmth.
Make it yours
The paired geometric pieces suit an anniversary buffet as easily as a winter table. Set out twelve small plates and let guests add their own mushrooms rather than balancing a topped diamond in one hand.
Ingredient labels
Check the polenta, stock and mustard labels for wheat, celery, soy and other allergens. The soy-drink variation contains soy.
A useful detail
The 250-minute finished-dish plan includes roasting, cooking and spreading, a short steam-release period, at least 2 hours of refrigerator chilling, cutting and the final hot bake. For the cold transport route, plan about 220 minutes before departure: cook and shallow-chill the mushrooms during the slab’s cold-set, and check both are at 40°F (4°C) or below before packing. At the gathering allow about 25–30 minutes for the final triangle bake and mushroom reheating to 165°F (74°C). Actual cooling may take longer. Choose the stated quick-polenta product rather than forcing a different liquid ratio or long-cook product onto this clock.
Another way
- Use 400 g peeled sweet potato instead of squash; roast and mash it fully before adding.
- Replace the milk with 300 ml unsweetened soy drink suitable for cooking, and the butter with 15 g olive oil. This changes the allergen list to include soy and does not make every brand otherwise allergen-free.
Keep it well
Refrigerate the cooled slab and cooked mushroom topping separately at 40°F (4°C) or below for up to 2 days. Once baked and assembled, use leftovers within the same original 2-day window, not 2 additional days. Reheat to 165°F (74°C). Respect the combined travel-and-display limit in “Bring it.”