Gluten free Thin Mints

5 tablespoons unsalted butter
4 ounces semi-sweet chocolate
¼ teaspoon pure vanilla extract
½ teaspoon pure peppermint extract
¾ cup (105g) high-quality all-purpose gluten-free flour
¼ teaspoon xanthan gum
½ cup (40g) unsweetened natural cocoa powder
¼ teaspoon baking soda
½ teaspoon kosher salt

GLAZE
½ pound semi-sweet chocolate, chopped
pure peppermint extract, to taste