Rinse a tart form or similar (diameter 28 cm) with cold water. Roll out the puff pastry a little larger, cover the shape with it, distribute the remnants of the pastry on top. Put the mold in the refrigerator. Preheat the oven to 210 degrees (convection 190 degrees).

Grate the cheese in two 100 gram portions. Roughly chop the walnuts and rinse the apple.

Whisk the eggs in a bowl and stir in the cream, mustard and 3 tablespoons of chives. Then stir in 100 grams of cheese and the walnuts. Remove the core from the apple, cut into small schnitzel and mix in.

Take the tart pan out of the refrigerator and prick the dough several times with a fork. Spread the cheese and egg mixture on the dough base, season with salt and pepper and spread the rest of the cheese over it.

Bake for 35 minutes on the lower rack until golden brown. Let rest a little before cutting. Sprinkle with the rest of the chives.