Preheat the oven to 180°C (350°F) and line a baking sheet with parchment paper.
Cream the butter and icing sugar together in a mixer for 2 minutes until smooth.
Add the egg yolk, baking powder, and banana extract. Beat for 30 seconds until fully combined.
Gradually add the flour and knead well by hand until a smooth dough forms—it should be neither too soft nor too firm.
Fold in the chocolate chips and knead briefly until evenly distributed throughout the dough.
Shape the cookies by scooping 2 tablespoons of dough, rolling it into a short log, and gently curving the ends into a crescent shape.
Arrange the crescents on the prepared baking sheet, leaving a little space between each one.
Bake for 18–20 minutes, or until the cookies turn lightly golden. Keep a close eye on them so the edges do not burn.
Cool and serve: Remove from the oven and dust the warm cookies with a first coating of sifted icing sugar so it sticks. Once they have cooled down, add a second dusting for a signature snowy-white appearance; a great little trick for beautifully finished crescent cookies!