Preheat the oven to 350F (180C).
Finely chop the onion, sauté it in a pan with the knob of butter and the tablespoon of oil, add a pinch of salt and pepper.
When they are golden, add the bacon and lightly brown it.
Remove from heat and pour in the tablespoon of thick cream.

In a bowl, whisk the eggs, flour, and baking powder.
Gradually incorporate the oil and warm milk.
Add the grated mozzarella and mix.

Incorporate the onion, bacon, and cream mixture into the base.
Pour everything into an ungreased mold and bake in the oven for 45 minutes.