Preheat your oven to 350°F (180°C) and line a baking sheet with parchment so the croissants don’t stick.

In a mixing bowl, beat the softened butter and granulated sugar until pale and fluffy, the aroma light and creamy against the spoon.

Crack in the eggs one at a time, stirring each in until fully incorporated and the mixture looks smooth and glossy.

Fold in the almond flour, all-purpose flour, almond extract, vanilla extract and lemon zest if using, mixing until a soft, thick frangipane batter forms.

Slice each croissant lengthwise about three-quarters of the way through, like opening a book, taking care not to cut all the way through.

Spoon generous amounts of the almond frangipane into the center of each croissant, spreading it evenly so it fills the pocket and peeks out slightly at the edges.

Press the croissant halves gently together so the filling stays nestled inside and the pastry still holds its shape.

Place the filled croissants on the prepared baking sheet, spacing them slightly apart for even air circulation.

Sprinkle the tops with sliced almonds, the nuts adding both texture and a golden, toasty look once baked.

Slide the tray into the oven and bake for 15–18 minutes, or until the croissants are puffed, golden-brown and the almond filling is set.

While the croissants bake, whisk powdered sugar with milk or orange juice in a small bowl until you achieve a smooth glaze that’s pourable but thick enough to coat.

Remove the croissants from the oven and let them cool slightly before drizzling the glaze over the warm pastries, letting it settle into every flaky layer.

Let cool a few minutes longer so the glaze sets, then serve warm for maximum aroma and texture.