Preheat your oven to 350°F (175°C) and line an 8×8-inch baking pan with parchment paper.

In a small saucepan, melt the unsalted butter over low heat until just melted, about 2-3 minutes. Allow to cool slightly before combining with light brown sugar.

Add eggs to the butter-sugar mixture one at a time, whisking well after each addition. Mix in both vanilla and almond extracts.

In a separate bowl, whisk together the all-purpose flour, baking powder, and salt. Fold into wet ingredients until just combined.

Combine almond flour and granulated sugar in a small bowl. Beat in an additional egg until filling is smooth and creamy.

Spread blondie batter evenly in the prepared baking pan. Spoon dollops of frangipane filling over the batter and swirl together gently.

Sprinkle sliced almonds over the top and bake for 30-35 minutes until golden and a toothpick comes out with moist crumbs.

Remove from oven, cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely. Dust with powdered sugar and enjoy!