In a small bowl, mix the unflavored gelatin with 2 tablespoons of cool water. Let it sit for about 5 minutes to bloom.
In a saucepan over medium heat, combine the bloomed gelatin, 1/4 cup plus 2 tablespoons of water, light corn syrup, granulated sugar, and kosher salt. Stir until the sugar dissolves and the mixture comes to a gentle boil. Remove from heat and let it cool slightly.
In a stand mixer, beat the 2 1/2 sticks of unsalted butter on medium speed until creamy and smooth. Gradually add the warm sugar mixture to the butter and mix until fluffy. Scrape down the sides of the bowl and add the vanilla bean or extract. Mix until combined.
In a separate bowl, whisk together the sifted cake flour, baking powder, baking soda, and salt. In another bowl, mix the soft unsalted butter, coconut oil, and granulated sugar until light and fluffy. Add the egg whites, vanilla extract, and almond extract, mixing until combined.
Gradually add the flour mixture and cultured low-fat buttermilk to the butter mixture, alternating between the two, starting and ending with the flour. Mix until just combined.
Preheat your oven to 350°F (175°C). Line a cupcake pan with liners and fill each liner about halfway with the batter. Add a spoonful of sprinkles to the center of each cupcake before topping with more batter until the liners are about two-thirds full.
Bake in the preheated oven for 15-18 minutes, or until a toothpick inserted into the center comes out clean. Allow the cupcakes to cool in the pan for a few minutes before transferring to a cooling rack.
Once the cupcakes are completely cooled, use the marshmallow buttercream to frost each cupcake generously. Top with additional sprinkles for that extra pop of color.
