Prepare the dry ingredients - Combine the almond flour and powdered sugar in a food processor and pulse until they are well-combined and finely ground. Sift the mixture into a large mixing bowl. If using ube powder instead of Ube spread, sift it into the mixture as well. - Be careful when pulsing the ingredients in the food processor as over-processing can lead to oily, grainy macaron shells.

Make the meringue - In the bowl of a stand mixer, start whipping the egg whites on low speed. Gradually add the granulated sugar one tablespoon at a time. Once the sugar has been added, increase the mixer speed to medium and continue whipping until you get stiff peaks. The meringue should be smooth, glossy, and able to hold its shape. - Be sure to use a clean bowl and clean utensils when making the meringue as any trace of grease or dirt can prevent the egg whites from whipping up properly. Also, make sure to add the sugar slowly over time, as this will help the egg whites stabilize and hold their shape better.

Fold the meringue into the dry ingredients - Add the Ube spread to the meringue and gently fold it in until it is well-combined. Add the meringue to the dry ingredients in two batches and use a spatula to gently fold them together. The mixture should be smooth and glossy, with no lumps or dry spots. - Be gentle when folding the meringue into the dry ingredients as over-mixing can lead to a flat batter and cracked shells. When adding the meringue to the dry ingredients, be sure to scrape the sides and bottom of the bowl to incorporate all of it.

Pipe and bake the macaron shells - Fit a piping bag with a round tip and fill it with the batter. Pipe 1.5-inch circles onto a baking sheet lined with parchment paper, leaving about an inch of space between each shell. Tap the baking sheet on the counter a few times to release any air bubbles and let the macarons rest for 30 minutes or until a skin forms on the surface. Bake the shells in a preheated oven at 300°F for 12-15 minutes. Let cool completely before filling. - Make sure to pipe the macaron shells with enough space between them to allow for spreading in the oven. To ensure even-sized shells, you can trace circles onto the parchment paper with a pencil or marker and use them as a guide while piping. When tapping the baking sheet to release air bubbles, do so gently to avoid deflating the batter.

Make the coconut buttercream filling - In a stand mixer fitted with a paddle attachment, beat the unsalted butter on medium speed until creamy. Gradually add the powdered sugar and beat until well-combined. Add the coconut milk, vanilla extract, and salt, and continue to beat until the mixture becomes light and fluffy. - Make sure the butter is softened to room temperature before beating it, as this will make it easier to cream. Gradually adding the powdered sugar will prevent it from flying out of the bowl and making a mess. When adding the coconut milk, make sure to only add a small amount at a time to prevent the mixture from curdling.

Fill the macaron shells - Match up the macaron shells by size and spread a heaping teaspoon of coconut buttercream onto one shell. Top it with another shell and press gently to sandwich them together. Repeat with the remaining shells. Refrigerate the macarons for at least an hour before serving to allow the flavors to develop. - When piping the filling onto the shells, make sure not to overfill them as this can cause the filling to ooze out the sides. Refrigerating the macarons before serving will make them easier to handle and will allow the flavors to meld together.