1 cup confectioners' sugar
1/4 teaspoon salt
2 teaspoons pure vanilla extract
2 1/2 cups all-purpose flour
- Preheat oven to 350 degrees F. Line baking sheets with parchment paper.
- In the bowl of an electric mixer fitted with the paddle attachment, beat together butter, confectioners' sugar, salt and vanilla on medium speed until smooth, about 2 minutes.
- Beat in the flour, beginning on low speed and increasing to medium until just combined.
- Form balls using 2 teaspoons of dough for each. Place balls 1 inch apart on baking sheets. Bake 10 minutes, remove from oven and press thumb into cookies (a 1/2 teaspoon measuring spoon also works) to make deep, wide indentations. Rotate pan and return to oven beat until light brown at the edges, 7 to 9 minutes more. If the indentations begin to lose definition, remove cookies from oven and press again. Transfer to a wire rack to cool completely.
- Warm cookie butter slightly so that it's easy to pour. Fill indentations with lukewarm cookie butter and let cool completely.