Caramelized Onion and Gruyere Pie

Peel the onion and cut it into large rings. Chill 80 g of butter in the freezer.

Heat the remaining butter in a pan together with olive oil. Place the onion in the butter foam and cook, stirring, for 25 minutes until it becomes golden brown.

Remove from heat, add thyme, 0.5 tsp salt and pepper. Let cool.

Mix the cooled onion with 85 g of grated cheese. Spread the mixture over the bottom of a 24 cm diameter glass baking dish.

In a food processor, mix flour, baking powder, baking soda and remaining salt. Add 55 g of grated Gruyère.

Cut cold butter into pieces and add to the dry mixture. Mix until it resembles coarse crumbs.

In a separate bowl, mix buttermilk and mustard. Add to the batter and stir until a thick mass forms, but do not mix completely.

Place the dough on a floured surface, knead it lightly, and shape it into a ball. Wrap it in plastic wrap and let it rest for 10 minutes at room temperature.

Roll out the dough between two pieces of plastic wrap into a circle 25 cm in diameter. Remove the top layer of plastic wrap and cover the baking form with the dough and onion.

Remove the bottom layer of film and carefully fold the edges of the dough into the mold.

Place the pie in the middle of the oven preheated to 200°C. Bake for 25–30 minutes until the crust becomes golden brown and firm.

Let the cake rest in the pan for 2 minutes. Cover with a dish and carefully turn it over. Serve warm.