https://www.delish.com/cooking/recipe-ideas/a20138735/butter-cookies-recipe/

Step 1
Preheat oven to 375° and line two large baking sheets with parchment paper. In a medium bowl, whisk together flour and salt.
Step 2
In a medium bowl using a hand mixer, beat butter and sugar until light and fluffy, 4 to 5 minutes. Add egg and almond or vanilla extract if using and beat until combined. Gradually add the flour mixture and beat until just combined. Divide dough in half.
Step 3
In a small bowl, beat egg yolk with two teaspoons water. On a floured surface, roll each dough out evenly to 1/4" thick. Punch out rounds with a 2" cookie cutter, placing them about 1" apart on prepared baking sheets. Use the tines of a fork to create a crosshatch pattern on the cookies, then brush tops of cookies with egg wash.
Step 4
Bake 10 to 12 minutes, until edges are beginning to turn golden. Cool completely before serving.