grapefruit sandwich cookies

My friend Elizabeth and I wanted to make some cookies, so we modified a recipe on epicurious to make these amazing grapefruity confections.

Grapefruit Sandwich Cookies
(makes about 24 sandwiches)

Filling:
3 tablespoons grated grapefruit peel
1/4 teaspoon salt
1 cup (2 sticks) unsalted butter, at room temperature
4 cups (packed) powdered sugar
4-6 drops red food coloring
...for less filling, halve this recipe and you should be ok for sandwiching, but honestly who would want less of this stuff?

Cookies:
1/2 cup fresh grapefruit juice
1 tablespoon finely grated grapefruit peel
3 3/4 cups all purpose flour
1 teaspoon salt
1/2 teaspoon baking soda
1 cup (2 sticks) unsalted butter, room temperature
1 1/2 cups sugar
2 large eggs
2 large egg yolks

For filling: 
Using back of spoon, mash grapefruit peel and salt to paste in medium bowl. Add butter. Using electric mixer, beat until fluffy. Add sugar in 4 batches, beating after each addition until blended.

For cookies: 
Boil grapefruit juice and peel in small saucepan until mixture is reduced to 2 tablespoons, about 4 minutes. Pour into small bowl and cool. Sift flour, salt, and baking soda into medium bowl.
Using electric mixer, beat butter in large bowl until fluffy. Add sugar; beat until blended. Beat in eggs, 1 at a time, then beat in yolks. Beat in grapefruit juice mixture. Add dry ingredients and stir to blend well. Cover dough and chill until firm, at least 4 hours and up to 1 day.
Preheat oven to 375°F. Line 2 baking sheets with parchment paper. Roll out 1/3 of dough on lightly floured surface to scant 3/8-inch thickness. Using 2-inch round cutter (or a squirrel-shaped one from IKEA, same thing obviously), cut out cookies. Transfer cookies to prepared baking sheets. Bake cookies, 1 sheet at a time, until golden at edges, about 12 minutes. Let cookies cool 5 minutes. Transfer to racks and cool completely. Repeat with remaining dough.

Spread 2 teaspoons filling on flat side of 1 cookie. Top with another cookie, flat side down. Repeat to make more sandwich cookies. Eat and pretend that calories are a myth, like Bigfoot.

Oh, and they're GREAT with milk. Elizabeth would like to share the quote, "I am going to kidnap your milk."