Preparing to bake: Heat the oven to 375 degrees F. Grease two 12-cup muffin tins. (For best results, use cupcake liners here.)
Combining the dry ingredients: Whisk together the flour mix, the psyllium, baking powder, baking soda, and salt. Set aside.
Creaming the butter and sugar: Put the butter into the bowl of a stand mixer. Using the paddle attachment at medium speed, whirl the butter and sugar together until they are thoroughly combined, creamy, and fluffy, about 3 minutes. Be sure to scrape down the sides of the bowl with a rubber spatula once in a while.
Combining the wet ingredients: Whisk together the eggs, egg yolks, and vanilla extract. Set aside.
Finishing the batter: With the stand mixer running, add the egg mixture, one tablespoon at a time, to the creamed butter and sugar. When the entire mixture is incorporated into the butter and sugar mixture, add 1/3 of the dry ingredients to the bowl. When there is no visible sign of flour, add 1/2 of the buttermilk. When that is incorporated, repeat this process, ending with the dry ingredients.
Baking the cupcakes: Using a small ice cream scoop, spoon enough cake batter into the prepared muffin tins to fill each one 2/3 of the way. Put the tin into the oven and bake until the cupcakes are slightly firm to the touch and a toothpick inserted into the cupcakes comes out clean, 20 to 30 minutes.
Allow the cupcakes to cool in the tins for 15 minutes. Run a butter knife around the edges of the cupcakes, then turn them onto a cooling rack.
Pour all the flours into a large container. (Restaurant supply stores sell large plastic containers that fit this purpose well. You could also use a large glass jar.) Shake and shake and shake harder until all the flours have become one color.
Variations: If you cannot eat dairy, try this with vegan "buttery" sticks and a non-dairy buttermilk. Suggestions: This recipe makes kid-approved cupcakes. But it also makes a lovely 2-layer cake.