Dough:
400 g all-purpose flour (about 3.2 cups)
100 g cornstarch (about ¾ cup)
2 eggs
100 g powdered sugar (about ¾ cup)
16 g vanilla sugar (about 1 tablespoon)
250 g cold butter, diced (about 1 cup)
½ tsp baking powder
Filling:
1 cup milk
½ cup sugar
3 egg yolks
a pinch of salt
3 tbsp all-purpose flour
230 g softened butter (about 1 cup)
3 tsp nut liqueur, rum, or vanilla extract
½ cup ground walnuts
Combine all the ingredients in a mixing bowl.
Alternatively, you can do this by hand.
To do so, cut the butter into the flour, add the remaining ingredients, and knead the dough.
Chill the dough in the refrigerator for 30 minutes.
From the chilled dough, form small balls and bake the cookies.
For the filling:
Mix the milk with half of the sugar and bring it to a boil.
In a mixing bowl, whisk the egg yolks, salt, the remaining sugar, and vanilla until pale.
Add the flour and whisk again.
When the milk comes to a boil, pour 1/3 of it into the egg yolk mixture and whisk.
Then transfer this mixture back into the pot with the milk and cook until it thickens like a pudding.
Remove from heat, cover with plastic wrap, ensuring it touches the surface of the mixture to prevent a skin from forming.
Let it cool.
Whip the butter until fluffy.
Gradually add the cooled mixture, one spoonful at a time, while continuing to whip.
Finally, fold in the walnuts.
Fill the cookies with the cream.