In a saucepan set over medium heat, combine the frozen raspberries and ¼ cup granulated sugar. Cook for approximately 10 minutes, stirring consistently, until the fruit breaks down and the mixture becomes syrup-like, though slightly chunky.

Set a mesh strainer over a bowl and pour the mixture through it, pressing gently to extract the liquid. Allow the syrup to cool completely. You should obtain 2–3 tablespoons of syrup.

Measure ½ cup frozen raspberries and chop them into small pieces. Place the chopped raspberries back into the freezer until ready to incorporate.

In a medium bowl, whisk together the gluten-free flour, baking powder, 1.5 tablespoons cornstarch, and kosher salt. Set aside.

In a small bowl, combine the rounded 2 tablespoons of cornstarch with 3 tablespoons water, stirring until the mixture becomes smooth and thin.

In the bowl of an electric mixer fitted with the paddle attachment, cream the softened butter (or vegan baking stick) with 1 ¼ cups granulated sugar for 2–3 minutes, or until light and creamy.

Add the cornstarch-water mixture, milk, and cooled raspberry syrup to the creamed butter mixture, beating briefly until combined. The mixture may appear slightly uneven in texture.

Gradually add the dry ingredients, mixing on low speed until just combined.

If desired, incorporate 3 drops of red food coloring and mix briefly to distribute the color throughout the dough.

Using a spatula, gently fold in the frozen chopped raspberries. Avoid overmixing, as the berries will release excess liquid if handled too aggressively.

Cover the bowl with plastic wrap and freeze the dough for at least 1 hour. This step is essential to prevent the cookies from spreading excessively during baking.

After 1 hour of freezing, preheat the oven to 325°F (163°C). Line a baking sheet with parchment paper.

Using a large cookie scoop (approximately 2 ounces), portion the dough into 12 balls.

Roll each dough ball in the reserved 2 tablespoons of granulated sugar until fully coated.

Place the dough balls on the prepared baking sheet, spacing them 3–4 inches apart.

Bake for 15 minutes.

Remove the cookies from the oven and immediately use a spatula to gently reshape the edges into uniform circles.

Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a cooling rack. Repeat the process with remaining dough, keeping unbaked portions in the freezer between batches.