In a mixing bowl or the bowl of a stand mixer, whisk the butter and sugar at medium-high speed for 2-3 minutes until you achieve a light and fluffy mixture.
Add the egg, almond extract, and vanilla. Mix at medium speed until fully incorporated. Scrape the sides and bottom of the bowl with a spatula if necessary.
In a large bowl, sift the flour, cornstarch, baking powder, and salt. Gradually incorporate this dry mixture into the butter/sugar mixture at low speed until just combined. Avoid overworking the dough.
Divide the dough into 3 equal parts (about 305 g each).
Leave one part natural (white). Color the other two parts with green and red food coloring.
Pro tip: Use gel coloring to avoid altering the texture of the dough.
Wrap each part in plastic wrap, flattening them into rectangles of 0.8 cm thick to ease rolling after refrigeration.
Unwrap each dough and roll them out on plastic wrap into rectangles of 18 x 30 cm
Use a rolling pin to seal the layers and achieve an even thickness.
Trim the edges with a sharp knife for clean lines. Slightly tilt one long side to create a more pronounced spiraled effect when rolling.
Roll the dough into a tight log, using parchment paper to assist in the operation. Seal the seam with your fingers while gently spreading the green dough.
Pour the Christmas sprinkles onto a tray. Roll the dough log in the sprinkles, pressing slightly for perfect adherence.
Cut into 0.8 cm thick slices with a sharp knife. If the dough becomes too soft, return it to the refrigerator for 15-30 minutes.
Place the sablés on the trays, spacing them 2.5 cm apart (they will spread slightly while baking).
Place the trays in the oven.