Not-Quite-Bonnie's Rugelach

Ingredients:
1 1/4 cups (160 g) all-purpose flour
1/8 tsp salt
1/4 tsp baking powder
Finely grated zest of 1 small lemon (3/4 tsp)
Scraped seeds of 1/4 vanilla pod
1/2 cup plus 1 tbsp (125 g) unsalted butter, fridge-cold, cut roughly into 1-inch/3-cm cubes
4 1/2 oz (125 g) cream cheese, fridge-cold
1/3 cup (40 g) walnut halves
1/2 packed cup plus 1 tbsp (100 g) light brown sugar
1/2 tsp ground cinnamon
5 1/4 oz (150 g) store-bought quince paste (membrillo)
1 tsp lemon juice
1 large egg, lightly beaten
1/2 tbsp demerara sugar

Instructions:
To make the pastry, place the flour, salt, baking powder, lemon zest and vanilla seeds in a food processor and pulse for about 15 seconds to combine. Add the butter and pulse for a few seconds more, until the mixture has the texture of fresh breadcrumbs. Add the cream cheese and process just until the dough comes together in a ball around the blade; be careful not to overprocess or the pastry will be tough. Tip the dough onto a lightly floured work surface and knead for a few seconds, just to bring it together.
Divide the pastry in two, cover each half loosely in plastic wrap, then press to flatten into disks. Transfer to the fridge for 1 hour.
Preheat the oven to 350°F/180°C. Line two baking sheets with parchment paper and set aside.
To make the filling, spread the walnuts out on a rimmed baking sheet and roast for 5 minutes. Remove from the oven, set aside to cool, then chop finely and place in a small bowl with the brown sugar and cinnamon. Mix together and set aside.
In a separate bowl, combine the quince paste and lemon juice to form a smooth paste. (If your quince paste is very firm, warm it gently over low heat to soften [or heat for 10 seconds in a microwave], until the texture is thick like jam but spreadable, then set aside to cool before using).
Take one of the pieces of dough from the fridge and roll out on a lightly floured work surface to form a 9 1/2-inch/24-cm circle, about 1/8 inch/3 mm thick. Use a small spatula or the back of a spoon to spread half of the quince paste evenly over the surface and then sprinkle with half of the sugar-nut mixture. Using a sharp knife or a pizza wheel, if you have one, cut the dough as though you are slicing a cake into twelve equal triangles. The best way to get even-sized triangles is to cut it first into quarters, then each quarter into thirds. One at a time, roll each wedge quite tightly, starting from the wide outside edge and working toward the point of the triangle, so that the filling is enclosed. Place them on the lined baking sheets, seam side down, spaced about 1 inch/3 cm apart. Repeat the rolling process with the remaining disk of dough and filling, then chill the rugelachs in the fridge for 30 minutes before baking.
Increase the oven temperature to 400°F/200°C.
When ready to bake, lightly brush the tops of the rugelachs with the beaten egg and sprinkle with the demerara sugar. Bake for 20–25 minutes, rotating the sheets halfway through, until golden brown all over. Don’t worry if some of the filling oozes out; this will add a lovely toffee taste to the edges of the cookies. Remove from the oven and allow to rest on the sheets for 5 minutes before transferring to a wire rack to cool completely.
The pastry can be made a day ahead and kept in the fridge, or frozen for up to 3 months (remember to thaw it overnight in the fridge before using). The rolled rugelach can also be frozen (before glazing) for up to 3 months. When you are ready to bake them, brush with the glaze and bake from frozen, adding an extra minute or two to the cooking time.
These will keep for up to 4 days in an open container, separated by pieces of parchment paper, and the whole thing wrapped loosely in aluminum foil. Don’t keep in an airtight container; the sugar will weep if you do and turn the rugelach soft and sticky.