1. Stir flour, baking powder and salt into a bowl. Add dark brown sugar, speculaas spice mix, butter and milk and knead until a dough forms.
2. Wrap the dough in cling film and leave to rest in the fridge for at least 30 minutes.
3. Preheat the oven to 350ºF. Line a baking tray with parchment paper.
4. Lightly whisk the eggs. Crumble the almond paste into a bowl. Add a little over half the egg to the almond paste. Mix the egg with the almond paste until fully incorporated.
5. Take the dough out of the fridge and divide it into two equal pieces. Roll out both pieces into a rectangle of approximately 6 inch x 12 inch. (You can roll out the dough on some cling film to make it easier to transfer).
6. Transfer one of the pieces of dough onto a baking tray lined with parchment paper. Spread the almond paste mixture on the dough, make sure to leave a little space on the sides.
7. Take the second piece of dough and place that onto the dough with almond paste. Seal the almond paste by tucking in the edges of the dough. Brush the dough with the remaining egg.
8. Decorate the gevulde speculaas with halved almonds. Bake in the oven for roughtly 40-45 minutes, till golden.