Preheat the oven to 350 degrees F. Line a half sheet pan with parchment paper. Butter the entire pan with 1 tablespoon of the butter. Using an electric mixer, fitted with a paddle attachment, cream the remaining 1 1/2 sticks of butter and 2 1/2 cups sugar together. Zest the oranges over the bowl and mix thoroughly, reserving the oranges. Add the eggs 1 at a time, and mix well. Sift the flour, salt and baking powder. Add the flour alternately with the milk. Mix well. Add the vanilla. Pour into the prepared pan. Place in the oven on the middle rack. Bake until the top is golden and the cake springs back, about 25 minutes. Remove from the oven and cool for 5 minutes in the pan. Place a piece of parchment paper over the rack and carefully invert the cake onto a wire rack. Allow the cake to cool completely.

For the orange syrup: In a saucepan, combine the juice of the oranges (about 1/2 cup) and the remaining 1 cup of sugar. Bring to a boil and cook for 2 minutes. Remove from the heat and cool completely. Brush the top of the cake with the orange syrup. Let the cake sit for 10 minutes. To assemble, cut the cake in half, crosswise. Spread the almond cream, evenly, over one cake. Place the other cake on top of the pastry cream and slightly press the layers together. Wrap in plastic wrap and refrigerate until the filling has set, about 2 hours. Using a serrated knife, trim of the edges of the cake and cut the cake into an even rectangle. Cut into individual cakes, 1 1/2 by 2 inches. Place the individual cakes on 2 wire racks, over a half sheet pan lined with parchment paper, about 2 inches apart from each other. In a mixing bowl, combine the powdered sugar, orange juice and some of the milk. Whisk until smooth. Pour the frosting over each cake letting the excess drip down the sides of the cake. Using a knife, spread the frosting evenly over the sides of the cakes. Sprinkle the top of each cake with the crushed almonds. Place the cakes back in the refrigerator and allow the frosting to set,