Nussecken (German Nut Corners)

To make the shortcrust base:

1. In the bowl of a stand mixer fitted with a paddle attachment or a large bowl, combine the flour, granulated sugar, vanilla sugar, baking powder, and salt.
2. Add the butter and pulse if using the mixer until the mixture becomes coarse and no pieces are larger than a pea. If using only a large bowl, cut the butter into the flour using a dough blade, your fingers, or forks.
3. Add the eggs and mix just until evenly combined and the dough comes together.
4. Form the dough into a disc, wrap in plastic, and refrigerate for 30 minutes.
5. Remove the dough from the plastic and place on a sheet of parchment about 12 inches (30.5 centimeters) wide and 16 inches (40.6 centimeters) long.
6. Lightly dust the dough with flour and roll into a thin sheet as close to exactly 9 inches (23 centimeters) wide and 13 inches (33 centimeters) long as possible.
7. Gently transfer the dough with the parchment paper to a 9x13 inch (23x33 centimeter) baking dish.
8. Press gently with your fingers to make sure the dough is even across the baking dish, filling in any edges or missing areas.
9. Prick the dough a few times with a fork.

To add the topping and bake:

1. Preheat oven to 350˚F (180˚C).
2. Use a pastry brush or spoon to spread the apricot jam evenly over the surface of the dough.
3. Place half of the hazelnuts (7 ounces/200 grams) in the food processor. Pulse until chopped, but not completely ground. Transfer to a bowl and set aside.
4. Place the other half of the hazelnuts (7 ounces/200 grams) in the food processor. Pulse just until ground into a flour. Transfer to the bowl with the chopped hazelnuts.
5. Place the 10 tablespoons (142 grams) butter, brown sugar, water, and vanilla sugar in a saucepan over medium low heat.
6. Stir the mixture until the butter has completely melted and the sugar has dissolved. Do not bring to a boil.
7. Remove from heat and stir in the hazelnuts until evenly combined.
8. Pour the hazelnut mixture over the apricot jam-covered dough. Use a spatula or spoon to spread the mixture evenly over the dough.
9. Place the baking dish in the preheated oven. Bake until the hazelnut topping is set and golden around the edges, 30-35 minutes.
10. Remove the baking dish from the oven.
11. Once slightly cooled, but still a little warm, use a sharp knife to carefully cut the sheet into thirds lengthwise (two equal lines) and fourths width-wise (three lines) to make 12 squares.
12. Cut each square diagonally to make 24 triangles in all. Allow the pastries to cool completely, about 2-3 hours.
13. Once the pastries have completely cooled, remove them carefully from the baking dish.
14. Place the chocolate in a bowl and microwave in 20 second increments, stirring in-between, until completely melted and smooth. Optionally, you could also melt the chocolate in a bain-marie/double boiler.
15. Dip the corners of each cooled pastry into the chocolate, allowing the excess to drip off.
16. Place the dipped pastry on a piece of parchment or wire rack to set.
17. Once set, carefully remove the pastries from the parchment using a paring knife or thin spatula.
18. Store the Nussecken in an airtight container at room temperature for up to a week.