Prepare the Oven and Pans: Preheat the oven to 350°F. Spray each individual cavity of the donut pan with cooking spray.
Combine the Dry Ingredients: Add the sifted flour, baking powder, and salt to a medium bowl. Whisk until evenly combined.
Mix the Wet Ingredients: In the bowl of a stand mixer, combine the buttermilk, sugar, lightly beaten eggs, melted butter, and vanilla bean paste. Beat until thoroughly mixed.
Make the Donut Batter: Add the dry ingredient mixture to the wet ingredients in three additions, beating only until each addition is incorporated. Do not overmix, as overbeating can make the donuts dry and tough.
Fill the Donut Pan: Transfer the batter to a piping bag. Pipe the batter into the prepared donut cavities, filling each one about two-thirds full to prevent overflowing during baking.
Bake the Donuts: Bake for 8 to 10 minutes, or until the tops spring back when lightly touched and a cake tester inserted into a donut comes out clean or with only a few crumbs attached.
Cool the Donuts: Let the donuts cool in the pan for 5 to 10 minutes. Carefully turn them out onto a wire cooling rack and allow them to cool completely before icing.
Prepare the Icing: In a medium bowl, whisk together the powdered sugar and vanilla bean paste. Add gel food coloring, if using. Gradually add the milk a few drops at a time until the icing reaches a thick, pourable consistency. It should be thick enough to stay on the donuts without dripping off, while still flowing like a thick liquid. Ice the Donuts: Transfer the icing to a piping bag and cut off the end. Pipe the icing over the completely cooled donuts. Immediately add sprinkles or other decorations before the icing begins to set.
Decorate in Small Batches: Ice and decorate only 2 or 3 donuts at a time, as sprinkles and other toppings will not stick once the icing has set.
Melt the Optional Chocolate: If making the optional chocolate decoration, place the white chocolate or white chocolate chips in a small bowl. Microwave in 20-second intervals until melted. Add a few drops of gel food coloring and mix until well combined.
Drizzle with Chocolate: Once the icing has set, place the donuts on parchment paper. Drizzle the melted chocolate over the tops in your preferred pattern, such as fine, straight lines made by moving the chocolate back and forth over each donut.
Finish the Decorations: While the chocolate is still tacky, add sprinkles and/or edible glitter. Allow the decorations to set before serving.