In a medium saucepan, combine your frozen raspberries and granulated sugar over medium heat. Stir continuously for 5–7 minutes until thickened. Remove from heat and cool.

In a mixing bowl, whisk together the gluten-free flour, cornstarch, baking powder, and kosher salt until combined.

Use an electric mixer to beat the unsalted butter and granulated sugar together for about 3–4 minutes until light and fluffy.

Add the cornstarch-water mixture, milk, cooled raspberry syrup, and optional red food coloring to the butter and sugar. Mix gently.

Gradually add the dry mixture to the wet mixture, stirring until blended. Fold in the chopped frozen raspberries.

Cover the bowl with plastic wrap and refrigerate the dough for at least 30 minutes.

Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

Using a tablespoon, scoop out portions of the dough and roll them into balls. Roll in sugar and space evenly on the baking sheet.

Bake for 10–12 minutes, until the edges are lightly golden. Allow to cool on the baking sheet before transferring to a wire rack.