Here's the recipe...the part about the egg yolk seemed very weird to me but it worked because the texture of the cookies was perfect.
French Butter Cookies
1 Large egg yolk, hard boiled
10 Tbs unsalted butter, softened
1/3 cup plus 1 Tbs sugar
1/4 tsp salt
1 tsp vanilla
1 1/2 cups flour
1. Press egg yolk through fine mesh strainer into a bowl of stand mixer. Add butter, sugar and salt. and beat on medium speed about 4 minutes. Turn mixer to low and add vanilla. Stop mixer and add flour. Mix on low until just combined, about 30 seconds.
2. Turn dough out onto parchment and press into a cohesive mass. (Dough will seem dry, but will hydrate in the fridge.) Divide dough in half and roll each piece into a log 6 inches log and 1 3/4 inches in diameter. Wrap each log in parchment, twist ends to seal and compact into a tight cylinder. Chill at least 1 hour. Dough could also be frozen for up to 2 weeks.
3. Preheat oven to 350F. Slice dough into 1/4 inch thick rounds. Place 1 inch apart onto parchment lined cookie sheets. Brush cookies with egg wash (1 egg white slightly beaten with 1 tsp water) and sprinkle with coarse (sanding) sugar.
4. Bake about 15 minutes, until edges are slightly browned. Cool on cookie sheet 5 minutes, transfer to cooling rack.
**For all of the cookies you see in the photo I made 2 batches of regular and one batch of chocolate (recipe follows).
For Chocolate Butter Cookies:
Follow recipe for regular, except reduce flour to 1 1/3 cups and add 1/4 Dutch-processed cocoa to flour.
For the sandwich cookie filling I simply melted some semi-sweet chocolate chips and spread it between two cooled cookies.
For the pretzels you roll the slices of dough into balls and then into 6 inch long snakes. Then you form into a pretzel shape and bake like normal.
For directions on how to form the spiral and checkerboard cookies I would use the illustrations and video on cooksillustrated.com as it is much more complicated to explain here.
The recipe turned out delicious and Embry loved helping make so many different shapes in one afternoon. We had some melted chocolate left over and we couldn't let it go to waste so we all agreed that it was best drizzled over the pretzels. Yum!
Other possibilities...adding lemon zest for lemon cookies, toasted coconut, or almond extract instead of vanilla. And don't get me started on the sandwich cookie fillings...