Step 1: Make the Raspberry Syrup

1. Combine frozen raspberries and granulated sugar in a small saucepan.
2. Cook over medium heat, stirring occasionally, until the raspberries break down and become syrupy (about 10 minutes).
3. Strain the syrup through a mesh colander to remove seeds. Cool completely.

Step 2: Prepare the Cookie Dough

1. Mix Dry Ingredients: In a bowl, whisk together gluten-free flour, cornstarch, baking powder, and salt.
2. Make Cornstarch Water: Mix 2 tablespoons of cornstarch with 3 tablespoons of water in a small bowl until smooth.
3. Cream Butter and Sugar: Beat butter with 1¼ cups of sugar in a large mixing bowl until light and fluffy.
4. Combine Liquids: Add cornstarch water, milk, and 3 tablespoons of raspberry syrup to the butter mixture. Mix well. If using food coloring, add it now.
5. Add Dry Ingredients: Gradually fold in the dry ingredients until combined. Fold in the chopped frozen raspberries.
6. Cover the dough and freeze for at least 1 hour.

Step 3: Shape and Bake

1. Preheat the oven to 325°F (163°C). Line a baking sheet with parchment paper.
2. Scoop dough into balls (12 total) and roll them in the remaining 2 tablespoons of granulated sugar.
3. Place dough balls on the baking sheet, spacing them 3–4 inches apart.
4. Bake for 15 minutes, or until edges are set. Let cookies cool on the baking sheet for 5 minutes before transferring to a wire rack.