Preheat the oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper, leaving some overhang on the sides for easy removal.
Make the cake base: In a large mixing bowl, add the melted butter, brown sugar, and granulated sugar and whisk until smooth. Add the eggs, vanilla extract, and almond extract and whisk until combined.
Mix in the baking powder, salt and almond flour. Beat well. Add the all-purpose flour and stir just until combined—do not overmix.
Spread the batter evenly into the prepared pan. Bake for 15 minutes while you prepare the almond cream.
Make the almond cream (frangipane): In a medium mixing bowl, mix the softened butter and sugar until smooth and creamy. Add the egg and almond extract and mix until incorporated. Fold in the almond flour until a thick almond cream forms.
Remove the partially baked base from the oven. Gently scoop the almond cream over the warm base and carefully spread it into an even layer. Sprinkle sliced almonds evenly over the top.
Return to the oven and bake for 25–30 minutes, or until golden brown and mostly set in the center. Avoid overbaking if you want a soft, gooey texture.
Let cool completely in the pan before slicing for clean bars. Dust generously with powdered sugar before serving.
