¼ cup sugar
1 teaspoon cinnamon
Using a stand mixer on medium speed, beat butter and sugar fluffy, about 2 minutes. Add yolk, sour cream, vanilla and salt. Beat fluffy again, about 1 minute. Add flour. On low speed, mix only until dough begins to clump, about 20 seconds.
Divide dough and pat into 2 disks. Settle one between 2 sheets of parchment paper. Roll dough 1/8-inch thin. Repeat with other disk. Slide dough (still in its paper, resting on a baking sheet) into freezer. Freeze firm, about 20 minutes.
Pull one sheet of dough out of the freezer. Peel off top sheet of parchment paper, pat it back into place. Flip dough and peel off the other sheet of parchment paper. Use a 2-inch round (or other shape) cookie cutter to punch out cookies. Pull away excess dough (the "negative space" between the cookies), leaving cookies on parchment, ready to bake. You can reroll and refreeze excess dough once. Repeat with remaining dough.
Stir together sugar and cinnamon to make topping. Sprinkle each cookie with cinnamon sugar. Slide into a 350-degree oven and bake until golden-brown, about 15 minutes.
Leah Eskin is a Tribune Newspapers special contributor. Email her at email@example.com.