Mix the flour, salt and grated Parmesan cheese. Add the butter in pieces and the egg yolk. Work the dough with your fingertips and add a spoonful of water if the dough is too dry. Place it in a cool place for 30 minutes, covered.
Preheat the oven to 180°c (th6). Roll out the dough, cut it with cookie cutters (e.g. into stars). Bake for about 25 minutes on the baking sheet covered with baking paper. Leave the shortbread to cool.
Rehydrate the gelatin in cold water. Peel and chop the onion and garlic. Peel and open the peppers, remove the walls and seeds and dice them. Fry them in an oiled pan, lower the heat and cook for 10m. Season
Mix the contents of the pan and add the drained gelatine to melt it. Then allow to cool completely. Whip the liquid cream into a firm whipped cream and add it to the pepper puree.
Line a pastry bag with this foam. Place it in a cool place for 30 minutes, then decorate the shortbread with it.