Peel and finely chop the onion. Clean, peel and wash the carrots. Cut into thin slices. Heat the oil in a pan, fry the carrots and onion for 1-2 minutes. Add peas and steam for 3-4 minutes, stirring several times.
For the puree, boil 375 ml water with 1/2 teaspoon salt. Pull the pot off the stove. Add cold milk and fat. Stir in the puree flakes well with a wooden spoon. Leave to swell for about 1 minute and stir again briefly.
Grease a casserole dish. Spread puree in it. Spread the vegetables over the puree. Whisk eggs with cream, season with salt and pepper and pour over the mixture. Sprinkle bacon and cheese over it. Bake in the preheated oven (electric cooker 225 °C/ convection oven: 200 °C/ gas: level 4) for about 15 minutes.
Serve garnished with chervil.