Preheat the oven to 180°C or 350°F convection.
Mix the chia seeds with the water in a glass and leave to swell.
Heat the butter in a saucepan. Add the sugar and stir until the sugar is fully dissolved. Remove the pot from the oven. Stir in the chia egg and grounded vanilla.
In another bowl, mix the remaining ingredients (except for the topping) and mix with the butter mixture to form a dough.
Finely chop the hazelnuts and toast them briefly in a pan without oil.
Roughly chop the white chocolate.
Line a baking sheet with parchment paper. Form 7-9 cookies of the same size (not too thin), place on the baking sheet and top with the white chocolate chips. Press the chocolate slightly into the Cookies. Bake for 10-12 minutes. Let it cool completely on the baking sheet.