In a large mixing bowl or bowl of a stand mixer, mix butter on high speed until smooth and creamy. Mix in the eggs, followed by the sugar. Add the flour and mix on low speed until just barely incorporated, with no dry spots remaining.

Flatten into discs. Wrap in clingfilm/plastic wrap and refrigerate until firm, at least 1 hour, or overnight.

Preheat oven to 350° F (176° C).

With a wooden rolling pin, roll dough very, very thin, less than 1/8-inch thickness. Dough should look almost translucent, but not be so thin that it tears when you move the cookies.

Cut shapes with a metal cookie cutter.

With a metal spatula, transfer cookies to a large, unlined, ungreased baking tray.

With a pastry brush, brush tops with a very thin layer of egg wash. Sprinkle with desired toppings.

Bake in preheated oven for 8-11 minutes, or until lightly brown around the edges.

Transfer cookies to a wire rack to cool completely. Repeat with remaining dough.

Store in an airtight container at room temperature for up to 2 weeks.