1 cup (2 sticks) plus 6 tablespoons unsalted butter, room temperature
1 cup confectioners' sugar
1/4 teaspoon salt
2 teaspoons pure vanilla extract
2 1/2 cups all-purpose flour
6 ounces semisweet chocolate, chopped
2 teaspoons corn syrup
1. Preheat oven to 350 degrees. Line two baking sheets with parchment paper.
2. In the bowl of an electric mixer fitted with a paddle attachment, beat together 1 cup (2 sticks) butter, the confectioners' sugar, salt, and vanilla on medium speed until smooth, about 2 minutes. Beat in flour, beginning on low speed and increasing to medium until combined. I do not have an electric mixer so I did this by hand. It turned out rather nicely.
3. Form balls using 2 teaspoons of dough for each. Place balls 1 inch apart on prepared baking sheets. Bake 10 minutes, remove from oven and press thumb into cookies to make a deep wide indentation. Rotate pan and return to the oven. Bake until light brown on the edges for another 7 to 9 minutes. Transfer to a wire rack to cool completely.
4. Instead of melting the chocolate like the book said to, I cheated and used the microwave. Here are the directions from the book. 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. Allow to cool a bit until slightly thickened. Fill thumbprints with the chocolate mixture, and set aside to firm up. Cookies can be stored in single layers in airtight containers at room temperature up to 3 days.