In a stand mixer or large bowl with a hand mixer, beat the butter on medium-high speed until light and fluffy. Add in the almond flour and sugar and cream for 1-2 minutes until light and fluffy
Add in the salt, extracts, and egg and continue to beat until evenly combined
Add in the milk and beat until just incorporated. Set aside
Orange blossom soak:
Add the sugar and water to a saucepan. Heat over medium heat until the sugar is dissolved. Remove from the heat and add the orange blossom water. Set aside
Assembly:
Preheat the oven to 350 degrees
Cut each croissant in half and place each half of the croissant cut side up. Using a pastry brush, soak each side liberally with the orange blossom sugar soak
Spread the 1/5 of the almond filling on the bottom half of each croissant. While filling, leave a ¼” border along the outside of the croissant (you should have 1/5 remaining after filling all 4)
Break each square (½ oz) of chocolate in 3 and place the pieces of chocolate in the center on top of the almond cream. Place the top back on the croissant
Split the remaining almond cream in 4 and place a quarter on top of each of the almond croissants. Spread the almond cream in an even layer until it covers the top
Scatter over ~1-2 tablespoons of slivered almonds. The almond cream will allow them to stick, but press them in slightly after scattering
Bake for 25 minutes or until golden
Let them cool for 15-20 minutes. Finish with powdered sugar