Combine the sugar, water, and almond extract in a small saucepan and bring to a simmer over medium heat, stirring to dissolve the sugar. Remove from the heat and let cool.

Place toasted almonds shallow bowl or pie pan and set aside.

In the bowl of a stand mixer fitted with the beater attachment, or with a hand mixer, beat butter, sugar, almond flour, and salt until well combined, about 2 minutes. Add almond extract and egg and beat until creamy. Place in refrigerator while you prepare the croissants. If making ahead, refrigerate and use within one week. If refrigerating, bring to room temp before assembling the croissants.

Slice croissants in half horizontally. Brush cut sides with almond syrup. Spread cut side of bottom pieces with about 2 tbs of frangipane. Replace the top half and spread with another 1-2 tbs of cream. Press croissant, top down, in the plate of almonds, adhering nuts to the cream. Place finished croissants on a parchment lined baking sheet.

Bake at 375° for 16-20 minutes, or until croissants are golden brown and almonds are toasted. Allow to cool for 10 minutes and then sprinkle with powdered sugar and serve.