Heat oven to 375° F. Line 2 baking sheets with parchment paper. In a large bowl, whisk together the flour, baking soda, and salt.
Using an electric mixer, beat the butter and sugars until creamy. Add the egg and vanilla and beat to combine. Gradually add the flour mixture, mixing until just incorporated. Fold in the peanut butter cups.
Drop tablespoon-size mounds 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.
This was a very dry cookie dough as you need the second egg, rule of the thumb in any basic Cookie recipe. Once this was corrected they seemed perfect. Baking nicely. So it was a good recipe.