Edited to say: I’ve made these again and tried them and they are amazing! One of my favorite cookies!
1 1/2 cups all-purpose flour
1 teaspoon baking soda
1/2 teaspoon kosher salt
1/2 cup (1 stick) unsalted butter, at room temperature
3/4 cup dark brown sugar
1/2 cup granulated sugar
1 large egg
1 teaspoon pure vanilla extract
1 12-ounce package small peanut butter cups, coarsely chopped
Heat oven to 375° F. Line two baking sheets with parchment or use a silicone mat. In a medium sized bowl, whisk together the flour, baking soda, and salt.
Meanwhile, beat together the butter and sugars until creamy. Mix in the egg and vanilla and beat to combine. Gradually add the flour mixture, mixing until just incorporated. Gently stir in the peanut butter cups.
Drop tablespoon-size amounts of dough 2 inches apart onto the prepared baking sheets. Bake until light brown around the edges, 12 to 15 minutes. Transfer to a baking rack to cool. Makes approximately 3 1/2 to 4 dozen cookies (depending on how big you make your cookies).