Toast almonds in Swiss roll tin for 10 minutes. Let cool. Grind finely 1/4 of the almonds, mix with 1/4 cup of the white sugar and set aside.
Grind coarsely the remaining 3/4 almonds and set aside. In a large bowl stir together flour, remaining 3/4 cup sugar, brown sugar, cinnamon and baking powder. Add the butter and stir until all ingredients are combined.
Stir in coarsely ground almonds and 2 of the eggs, then knead the dough in the bowl until all ingredients are combined. Divide dough in half.
Form each half into a 10x40cm rectangle. Transfer rectangles to baking trays which have been buttered and floured. Brush rectangles well with 1 egg combined with 2 tablespoons of milk. Sprinkle with reserved almond/sugar mixture. Bake them in the upper third of the oven for 20-25 minutes or until golden brown and skewer comes out clean. Cut rectangles crosswise into slices 2cm thick. Let stand 15 minutes in the turned-off oven. Transfer to racks and let cool thoroughly. Store airtight.