In a medium bowl, sift together the almond flour, millet flour, tapioca flour, baking powder, and salt. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment or a mixing bowl with a hand mixer, cream the butter and sugar together on medium high speed until light and fluffy, 3-5 minutes. Add the vanilla and mix until combined.

Add the eggs, one at a time, mixing just until combined after each egg, scraping down the sides and bottom as needed.

With the mixer on low, slowly add the dry ingredients. Increase the speed to medium and mix until just combined, scraping down the sides as needed.

Divide the dough in half and form into two discs. Roll out each disk between two pieces of parchment paper dusted well with millet flour to ⅛-1/4 inch thickness. Chill on a baking sheet for at least an hour in the fridge or 15 minutes in the freezer.

Working with one half at a time, use cookie cutters to cut out your shapes. Roll the scraps up with more millet flour dusted on the table and cut out cookies again, chilling the dough for 5-10 minutes as needed as the dough gets softer. Transfer your cut cookies to a parchment-lined baking sheet, 1.5 inches apart.

Chill the cookies on a parchment-lined baking sheet in the fridge for 30 minutes or in the freezer for 15 minutes.

Meanwhile preheat the oven to 400°F. One sheet at a time, bake the cookies for 5-7 minutes, until just set and the very bottom edges begin to turn golden. For softer centers, aim toward the lower end and crispy edges, the higher end (and this will vary depending on the size of your cookies!).

Let the cookies cool on the baking sheet for 5 minutes before using a thin metal spatula to transfer them to a wire rack to cool completely before icing. Repeat with remaining baking sheets.

While the cookies cool, make the icing. In a medium bowl, whisk the powdered sugar with 3 tablespoons of milk, honey, vanilla, and salt until smooth. Add another teaspoon of milk at a time until the icing is the proper consistency. When you lift the whisk up and drizzle icing back into the bowl, the stream should sit on top for a few seconds before incorporating back into the bowl. Divide icing between cups and color with gel food coloring as desired.

To pipe the icing, fill a small pastry bag fitted with a small round tip with icing. Pipe an outline around the outside of the cookie with icing. Begin to flood the outline with more icing using the tip or a toothpick to move the icing to the edges. Top with sprinkles and let sit for 10 minutes until the icing sets.

Enjoy immediately or, if you prefer softer cookies, store them in an airtight container overnight and enjoy them perfectly soft the next day. In my opinion these cookies are best on day 2!