Preheat the oven to 350°F (175°C) and line a 12-cup muffin pan with paper liners.
In a large mixing bowl, combine the gluten-free flour blend, granulated sugar, baking powder, baking soda, and salt. Whisk together until evenly mixed.
In a separate bowl, mix the almond milk and apple cider vinegar. Let it sit for about 5 minutes to curdle slightly.
Add the melted coconut oil and vanilla extract to the almond milk mixture, stirring until well combined.
Pour the wet ingredients into the dry ingredients. Stir gently until just combined, being careful not to overmix.
Spoon the batter into the lined muffin cups, filling each about two-thirds full.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Remove from the oven and allow the cupcakes to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
While the cupcakes cool, prepare the frosting. In a mixing bowl, beat the vegan butter until creamy.
Gradually add the powdered sugar, mixing on low speed until combined. Add 1 tablespoon of plant-based milk and vanilla extract, then beat until fluffy. If needed, add more milk to reach your desired consistency.
Once the cupcakes are completely cool, frost them generously with the vegan frosting.