Preheat oven to 350 F
Combine lemon juice and coconut milk - set aside for 10 minutes while you put together batter. This is your vegan "buttermilk."
Using a stand mixer with the whisk attachment, mix softened butter and oil together for 3 minutes or until well combined and homogenous.
Add granulated sugar slowly, allowing it to incorporate, then mix for another 3 minutes.
Tablespoon by tablespoon, add aquafaba/seltzer water mix, then vanilla extract. Beat for another 3 minutes.
In a separate bowl, sift dry ingredients.
In 4 batches, alternate adding the "buttermilk" (coconut milk and lemon) with dry ingredients, starting with buttermilk, and ending with dry ingredients.
If desired, stir in sprinkles. BEWARE the colors might bleed a bit.
Line your muffin pan with cupcake liners, and scoop batter into the liners. My scoop is ~¼ cup, maybe a little more.
Bake at 350 F for 20-30 minutes, testing with a toothpick or knife (when it comes out clean, your cupcakes are probably ready).
Cool in pan for 5-10 minutes, then on a cooling rack for at least 2 hours before frosting.
For the frosting:
Add softened butter, powdered sugar and vanilla extract to a stand mixer bowl with whisk attachment. Start on low, and build up speed as powdered sugar mixes in.
Transfer into a piping bag if desired, or ice using a knife or offset spatula. If icing is too thin, put in the freezer for 5-10 minutes.
Store frosted cupcakes in the refrigerator, and enjoy!