Mix all the ingredients for the gingerbread dough in a bowl. Once it's a cohesive ball, wrap it in plastic wrap and put the dough in the fridge for at least an hour.
Preheat the oven to 180 degrees.
Grease a mold and line it with baking paper. We used a square shape of 20x20 cm.
Divide the dough into two pieces. A piece of 2/3 and a piece of 1/3.
Roll out the largest piece on a floured work surface to about 1.5 cm thick.
Line the mold and the edges with the dough. Trim the edges neatly.
Mix the almond paste with water and make it a bit smooth.
Line the mold with the 2/3 layer of dough including the edges.
Cover the layer of dough with the almond paste so that there is an equal amount everywhere.
Roll out the other piece of dough and place on the almond paste. Fine-tune and trim here and there if necessary.
Brush the gingerbread with a mixture of egg and milk. Press the almonds into the dough, not too far, and brush again with the mixture and put in the oven.
Depending on your oven, you can bake the filled gingerbread in 35 minutes. Let cool on a wire rack and cut into cubes.