Prep the oven and pan: Heat the oven to 350°F (175°C). Line a baking sheet with parchment paper. This prevents sticking and helps the bottoms brown evenly.

Make the simple syrup: In a small saucepan, combine 1/2 cup water and 2 tablespoons sugar. Bring just to a simmer, stir to dissolve, then remove from heat. Add 1 tablespoon rum or amaretto if using. Let cool slightly.

Mix the frangipane (almond filling): In a bowl, beat 6 tablespoons softened butter with 1/2 cup sugar until creamy and light, about 1–2 minutes. Beat in 2 eggs, one at a time, until smooth. Add 1 cup almond flour, 1 tablespoon all-purpose flour, 1/2 teaspoon almond extract, 1 teaspoon vanilla, and a pinch of salt. Mix until just combined. If very thick, loosen with 1–2 tablespoons milk or cream. The texture should be spreadable, not runny.

Split and brush the croissants: Slice each croissant horizontally, like a sandwich. Lightly brush the inside and the cut surfaces with the cooled syrup. Don’t soak—a light coat keeps them moist without turning soggy.

Fill with almond cream and chocolate: Spread about 2 tablespoons of frangipane on the bottom half of each croissant. Sprinkle on a generous line of chopped dark chocolate. Top with the other half and press gently to secure.

Top and decorate: Spread a thin layer (about 1 tablespoon) of frangipane on top of each croissant. Sprinkle sliced almonds over the surface so they stick to the cream.

Bake: Arrange croissants on the prepared sheet. Bake for 18–22 minutes, until the tops are deep golden and the almonds are toasted. The filling should look set and slightly puffed. If edges brown too quickly, tent loosely with foil.

Finish: Let cool on the pan for 10 minutes. Dust with powdered sugar. Serve warm for melty chocolate, or at room temperature for a firmer bite.