-
1
Preheat oven to 350F.
-
2
Line two baking sheets with parchment paper.
-
3
In the bowl of an electric mixer fitted with the paddle attachment, beat together 1 cup (2 sticks) butter, the confectioners sugar, salt, and vanilla on medium speed until smooth, about 2 minutes.
-
4
Beat in flour, beginning on low speed and increasing to medium until combined.
-
5
Form balls using 2 teaspoons of dough for each; place balls 1 inch apart on prepared baking sheets.
-
6
Bake 10 minutes, remove from oven, and press thumb into cookies to make deep, wide indentations.
-
7
Rotate pan, and return to oven; bake until light brown on the edges, 7 to 9 minutes more.
-
8
(If the indentations begin to lose definition, remove cookies from oven and press again.)
-
9
Transfer to a wire rack to cool completely.
-
10
Combine chocolate, the remaining 6 tablespoons butter, and the corn syrup in a small heatproof bowl set over a pot of simmering water; stir occasionally until melted and smooth.
-
11
Allow to cool a bit until slightly thickened.
-
12
Fill thumbprints with the chocolate mixture, and set aside to firm up.
-
13
Cookies can be stored in single layers in airtight containers at room temperature up to 3 days.
