Preheat your oven to 325°F (160°C). Line a baking sheet with parchment paper to ensure easy removal and no sticking.
In a medium mixing bowl, combine the softened plant-based butter, granulated sugar, and vanilla extract. Beat them together until the mixture is light and fluffy.
Gradually add the gluten-free all-purpose flour blend to the wet ingredients, stirring until just incorporated. Next, slowly mix in the dairy-free milk, one tablespoon at a time, until a soft, workable dough forms.
If you're using fresh rosemary, gently fold the finely chopped leaves into the cookie dough until evenly distributed.
Scoop out approximately one tablespoon of dough for each cookie. Roll each portion between your hands to form smooth balls, then place them onto your prepared baking sheet.
Gently press an indentation into the center of each cookie ball using your thumb or the back of a small spoon.
Carefully spoon a small amount of apricot preserves into each thumbprint. If you like, sprinkle with colored sanding sugar for a beautiful, sparkly finish.
Place the baking sheet in the preheated oven and bake for 15 minutes, or until the edges of the cookies are lightly golden.
Remove the cookies from the oven and let them cool on the baking sheet for a few minutes to allow them to firm up. Then, carefully transfer them to a wire rack to cool completely before enjoying. They're best when fully cooled!