015 / 75 · Cupboard Suppers

Baked Onion and Oat Custard with Peas

4 generous custard squares, each with one 40 g slice of toast · Active 25 min · Total 1 hr 25 min

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Cooked onions and a handful of peas sit in a soft oat-and-egg custard with a little cheddar. The oats soak while the onions cook, then the oven does the setting. Cut it into four broad squares and serve each with toast: a quiet, savory supper made from ingredients that also work hard at breakfast.

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Hand-drawn baked onion and oat custard with green peas, a golden top and toast.

Soak flakes, not instant cereal

Plain rolled oats need time in the measured milk before the eggs are mixed in. This softens them without turning the mixture into a separately cooked porridge. Instant flavored oatmeal behaves differently and can add sugar or extra thickeners, so it is not an equivalent ingredient here. The finished square remains moist and spoon-tender, with visible oat flakes, rather than cutting like a dry breakfast bar.

Spend the active time on the onions

Onions are the main savory flavor, so cook them until soft and golden instead of stirring raw pieces into the dish. Moderate heat gives them time to sweeten without requiring a larger amount of cheese. Let them lose their fierce heat briefly before combining with the cold oat mixture. Meanwhile, beat the eggs thoroughly so the custard sets evenly rather than developing separate patches of white and yolk.

Check the center, then let it settle

Choose a two-liter baking dish with enough headroom for the mixture. A deeper, narrower dish can leave a liquid center after the edges have browned. Check the actual middle with a thermometer and give the cooked dish its short rest before serving; it firms as it stands. The toast is included in the portions, so there is no need to invent a collection of toppings to turn one square into a meal.

Ingredients

  • 1 cup plain rolled oats (80 g)
  • 2 cups milk (480 ml)
  • 1 tablespoon plus 1 teaspoon neutral oil (20 ml), divided: 15 ml for onions and 5 ml for dish
  • 2 medium onions, thinly sliced (300 g prepared)
  • 4 large eggs (200 g without shells)
  • 1 teaspoon prepared yellow mustard (5 g)
  • 3/4 teaspoon fine salt (4.5 g)
  • 1/4 teaspoon ground black pepper (0.5 g)
  • 1 cup frozen peas (140 g)
  • 1/2 cup grated cheddar (50 g), divided equally
  • 4 slices plain wheat bread, for toast (160 g total)

Set out

2-quart/2 L baking dish, about 8 inches/20 cm square and 2 inches/5 cm deep, mixing bowl and whisk, skillet, grater, measuring jug, food thermometer, oven mitts, toaster or grill

Allergens

egg, milk, wheat, mustard. Check labels and substitutions.

Make it

  1. Heat the oven to 350°F/175°C and grease the baking dish with 1 teaspoon/5 ml oil. Combine oats and milk in the bowl and leave for 20 minutes while preparing the onions.
  2. Heat the remaining 1 tablespoon/15 ml oil in the skillet over medium-low heat. Add onions and cook for about 15 minutes, stirring, until soft and golden. Let them cool in the skillet for 5 minutes.
  3. Beat the eggs thoroughly with mustard, salt and pepper. Stir into the soaked oats, then mix in onions, frozen peas and 25 g of the cheddar. Scrape into the prepared dish and scatter the remaining 25 g cheese over the top.
  4. Bake for 40–45 minutes, until the edges are set, the middle no longer looks liquid and the center reaches 165°F/74°C. Use the temperature and set center rather than surface browning alone.
  5. Rest for 10 minutes before cutting into 4 equal squares. During the rest, toast the 4 measured bread slices. Serve one custard square and one slice of toast per portion.

A measured accompaniment

The four bread slices belong to the base meal and yield. They are not extra uncounted serving suggestions.

Ingredient labels

Also contains prepared mustard. Check the prepared mustard, oats, bread and cheese labels for additional allergens; the base is not wheat-free.

A useful detail

The rest is part of the stated total time. Cutting straight from the oven gives a looser spoonful; the same dish holds a broad, soft square after ten minutes.

Another way

  • Replace the peas with 140 g frozen chopped broccoli, thawed and squeezed dry before mixing.
  • For individual portions, divide the mixture between 4 greased ovenproof dishes of at least 14 fl oz/400 ml capacity. Begin checking after 25 minutes and still verify 165°F/74°C in the center; total time will differ.

Keep it well

Refrigerate shallow portions within 2 hours, or 1 hour above 90°F/32°C. Keep at 40°F/4°C or below for up to 3 days and reheat to 165°F/74°C throughout. Store and toast the bread separately so it does not become damp against the custard.