If necessary, make caster sugar: You should use caster sugar for this recipe. If you don’t have any on hand (I never do), blitz your sugar in a blender or coffee grinder for 5 - 10 seconds to mill some of the sugar grains a bit more finely.
Cream your butter and sugar together. If you’re mixing by hand, it will help to leave the butter out to soften slightly, or blitz in the microwave for 5 - 10 second to very lightly soften it.
Make your potato starch “eggs” by thoroughly mixing potato starch and water. The ratio of potato starch to water is 1:2 (for one egg, 1 tablespoon potato starch + 2 tablespoon water). Add the starch eggs to the creamed butter and sugar and mix in.
Mix in almond flour and almond extract.
Notes
Caster sugar is worth the extra effort here! It dissolves better into the mixture and contributes a better texture. This sugar is finer than standard granulated sugar but courser than powdered sugar.