Muffins:

• 2 cups cake flour
• 1 1/2 tsp baking powder
• 3/4 tsp kosher salt
• 1/4 cup Rainbow sprinkles
• 1/2 cup buttermilk
• 1/3 cup grapeseed oil
• 2 tsp clear imitation vanilla extract (regular brown vanilla extract is ok if you're unable to source clear imitation, the result is an off-white cake and icing vs a pristine bright white batter)
• 1 1/4 cup granulated sugar
• 1/3 cup vegetable shortening
• 4 tbsp (1/2 stick) unsalted butter, room temperature
• 3 tbsp light brown sugar, packed
• 3 large eggs

Icing:

• 1/2 cup (1 stick) unsalted butter, room temperature
• 1/4 cup vegetable shortening
• 1/4 cup cream cheese, room temperature
• 2 tbsp light corn syrup
• 1 tbsp clear imitation vanilla extract (regular brown vanilla extract is ok if you're unable to source clear imitation, the result is an off-white cake and icing vs a pristine bright white icing)
• 1 1/4 cups powdered (icing) sugar
• 1/2 tsp kosher salt
• 1/4 tsp baking powder
• 1/2 tsp fresh lemon juice
• 2-4 tsp Rainbow sprinkles