Recipe: https://www.loveandlemons.com/sugar-cookies/#wprm-recipe-container-42239

For cookies:

In a medium bowl, combine the flour, baking soda, cream of tartar, and salt.

Cream the butter in the bowl of a stand mixer fitted with the paddle attachment. Add the sugar and beat until fluffy, scraping down the sides of the bowl as needed. Add the egg and beat well, then add the vanilla extract, almond extract, and lemon zest and mix again. Add the dry ingredients, one-third at a time, mixing until well combined. Divide the dough into two balls and flatten into disks. Wrap in plastic wrap and transfer to the fridge to chill for 2 hours.

Preheat the oven to 350°F and line two baking sheets with parchment paper.

Roll the dough on a lightly floured surface to ¼-inch thickness. Use cookie cutters to cut out desired shapes. Transfer to the baking sheets and bake, one sheet at a time, for 10 minutes. Let cool on the baking sheet for 2 minutes, then transfer to a wire rack to continue cooling. Cool completely before icing.

For icing:

Ingredients:
4 cups powdered sugar
3 tablespoons meringue powder
5 to 6 tablespoons water, more as needed

Sift the powdered sugar into the bowl of a stand mixer. Add the meringue powder and 5 tablespoons water. Mix until smooth and glossy. Transfer half of the frosting to a piping bag with a #3 tip for piping thin lines (i.e., the snowflakes) and for outlining filled-in shapes. For flooding/filling in cookie shapes, add more water, ½ teaspoon at a time, to thin the icing to a runny consistency.