1. Mix the flour, baking powder, and a pinch of salt. Incorporate 100 g of butter and the egg using your fingertips. As soon as the dough is homogeneous, wrap it and let it rest for 30 minutes in the refrigerator.

2. In a pan, cook the chopped onions for 10 minutes in oil with salt, pepper, and sugar over low heat, stirring with a spatula. Let cool.

3. Preheat the oven to 210°C.

4. Cut the gorgonzola into small slices.

5. Butter a tart mold with a removable bottom. Roll out the dough and line the mold.

7. Fill the tart with the onions. Sprinkle the walnut kernels and gorgonzola slices.

8. Bake the tart for 25 to 30 minutes.

9. Remove from the oven. Let rest for 5 minutes, unmold, and serve.