Juice 1 lemon and dice the apples. In a small saucepan, melt the butter, then add the sugar and cook over low heat until caramelized.

Once caramelized, add the diced apples and mix well. Pour in the lemon juice and stir gently over low heat.

Cook until the mixture is completely reduced. Stir slowly; if there's too much liquid, it won't wrap well! The puff pastry will become soggy. Once done, let it cool.

Let the puff pastry soften slightly, but not too much. Work quickly! Add the apple filling, and brush the edges with egg wash to seal. Fold and seal well, pressing with a fork, then make diagonal cuts on the surface.

Line a baking sheet with parchment paper, place the apple rolls on it, and brush the surface with egg yolk. Bake at 400°F (200°C) for 18-20 minutes. Oven temperatures may vary, so adjust accordingly!