Heat oven to 350℉.
Line sheet pans with parchment paper. Set aside.
With an electric mixer, beat butter, peanut butter, and sugar until light and fluffy, about 3-4 minutes.
Add egg and vanilla.
Beat until fully incorporated.
Add flour, baking soda, and salt.
Mix only to combine.
Divide dough into 1 teaspoon portions.
Roll into balls.
Place 2 balls ¼ inch from each other on prepared pan.
Flatten dough to ½ inch.
Use the tines of a fork to make crosshatch pattern on each cookie. (See photos above.)
Repeat for remaining dough.
Bake for 12 minutes, or until just starting to color.
Let cool on pan.