For the cookies:
- 4 sticks unsalted butter
- 1 1/2 cups granulated sugar
- 6 egg yolks
- 1 Tbs. vanilla extract
- 5 cups all-purpose flour
- 2 tsp. baking powder
- 1 tsp. salt
For the buttercream:
- 8 Tbs. (1 stick) unsalted butter
- 3 cups confectioners¿ sugar, sifted
- 2 Tbs. milk, plus more, if needed
- 1 tsp. vanilla extract
- 1/4 tsp. salt
- Food colorings (optional)
To make the cookies, in the bowl of an electric mixer fitted with the flat beater, beat together the butter and granulated sugar on medium speed until light and fluffy, about 4 minutes. Add the egg yolks one at a time, beating well after each addition. Beat in the vanilla.
In a sifter, combine the flour, baking powder and salt. Sift the flour mixture directly onto the butter mixture. Beat on low speed until well mixed.
Turn the dough out onto a work surface and divide into 4 equal portions. Shape each portion into a ball, then flatten the balls into disks. Wrap in plastic wrap and refrigerate until chilled, at least 4 hours or up to 2 days. Let the dough soften slightly at room temperature before continuing.
Place 1 dough disk between 2 sheets of waxed paper or parchment paper and roll out to 3/16-inch thickness. Refrigerate until firm, about 30 minutes.
Position a rack in the upper third of an oven and preheat to 350°F. Line several cookie sheets with parchment paper.
Dip Halloween cookie cutters in flour. Cut out an equal number of each shape, pressing an imprint on only half of the cutouts. Using a large metal spatula, transfer the cookies to the prepared pans. Gather up and reroll the scraps, refrigerate until firm and cut out more cookies. Repeat with the remaining dough disks. Refrigerate the cookies for 15 minutes before baking.
Bake the cookies until they are golden on the edges, 10 to 12 minutes. Transfer the pans to wire racks and let the cookies cool completely on the pans.
Meanwhile, make the buttercream: In the bowl of an electric mixer fitted with the flat beater, beat the butter on medium speed until light and creamy, 2 to 3 minutes. Reduce the speed to low, add the confectioners' sugar, the 2 Tbs. milk, the vanilla and salt, and beat until smooth and combined, about 2 minutes. Stop the mixer and scrape down the sides of the bowl. Increase the speed to medium and beat until fluffy, about 3 minutes.
If the frosting is dry, add more milk, 1 tsp. at a time, until it is creamy but still holds peaks. Tint with food colorings as desired.
For sandwich cookies: Spread 2 tsp. buttercream on top of the solid cookies. Top with an imprinted cookie and gently press together. Decorate the tops of the sandwich cookies as desired. Store the cookies in an airtight container at room temperature for up to 1 week. Makes about 24 sandwich cookies.
Adapted from Williams-Sonoma Kitchen Library Series, Holiday Baking, by Jeanne Thiel Kelley (Time-Life Books, 1995).