Preheat your oven to 350°F (175°C).
Grease two 9-inch round cake pans with butter or cooking spray and dust with gluten-free flour.
In a large mixing bowl, combine gluten-free flour, sugar, baking powder, and salt. Whisk thoroughly.
In another bowl, mix softened butter, eggs, vanilla extract, milk, and apple cider vinegar with an electric mixer for 2-3 minutes.
Gradually add wet ingredients to dry ingredients and mix on low speed until just combined.
Divide the batter evenly between the two prepared cake pans and smooth the tops.
Bake for 25-30 minutes, checking for doneness with a toothpick.
Let the cakes cool in the pans for 10 minutes, then transfer to wire racks to cool completely.