Syrup: In a small saucepan, heat sugar and water until dissolved, take off heat, let cool, and add vanilla extract. Set aside until ready to use.
Peanut Filling: In a medium mixing bowl, cream together butter and icing sugar. Add egg in three additions, mixing thoroughly after each addition.
Mix in flour and nuts until fully incorporated. Cover bowl with plastic wrap, chill until ready to use.
Assembly + Finishing
Set a rack in the middle of your oven, preheat to 375 degrees F / 180 C.
Cut croissants in half, like you would for a sandwich.
Brush the insides (top and bottom) with syrup twice so they soak up thoroughly. You might have some syrup left, depending how big your croissants are.
Spread about 2 tablespoons of peanut frangipane onto the bottom half of each croissant. Top with about 1 tablespoon of jam, make sure to cover whole surface area of the croissants.
Sandwich the croissants with the top half. Spread the leftover peanut frangipane on the tops, sprinkle with crushed peanuts.
Bake in the preheat oven for about 15-20 minutes, until the tops have browned nicely. Cool croissants before garnishing.
Spoon a little jam on the tops, garnish with strawberries. Finally lightly dust with icing sugar to finish.