Preheat the oven to 375 degrees.
In a stand mixer with the paddle attachment, mix softened butter and sugar until creamed, then mix in the almond paste.
Slowly add in the eggs one at a time, mixing well after each addition. Don't be in a hurry to add all of the eggs at once! This step adds air to the batter which is what gives the cake its amazing texture.
Once batter is smooth, add in the vanilla, salt, baking powder, and Poudre Douce. Then add in flour, mixing well and scraping down the sides of the bowl as you go.
Line a quarter sheet pan (9x13 inches) with parchment paper, then spray with pan spray. Spread the cake batter evenly with a spatula and bake for 30-40 minutes until golden brown.
Let cool, then cut into squares or triangles and serve with whipped cream and seasonal fresh fruit.