Preheat the oven as needed.

In a small saucepan, combine sugar, water, and 1/4 teaspoon almond extract; heat until sugar is dissolved.

In a mixing bowl, cream softened butter and granulated sugar together.

Add almond flour, egg, egg yolk, vanilla extract, remaining almond extract, and whole milk to the butter mixture; mix well.

Slice the day-old croissants in half, lengthwise.

Spread the almond filling inside each croissant and add chopped dark chocolate pieces.

Close the croissants and place them on a baking sheet.

Brush the tops of the croissants with the sugar syrup mixture.

Scatter sliced almonds on top of the croissants.

Bake in the oven until golden brown, about 15 minutes.

Dust with powdered sugar before serving.