Preheat the oven to 350°F (175°C). Lightly grease cookie sheets or line them with parchment paper.

In a medium bowl, cream together 1/2 cup butter, 1/2 cup white sugar, and 1/3 cup packed brown sugar until the mixture is smooth and slightly fluffy (about 1–2 minutes with a hand or stand mixer, or a little longer by hand).

Add 1/2 cup peanut butter and 1/2 teaspoon vanilla extract to the creamed mixture and stir until combined.

Add 1 egg and mix until the egg is fully incorporated and the batter is uniform in color and texture.

In a separate bowl, whisk together 1 cup all-purpose flour, 1 teaspoon baking soda, and 1/4 teaspoon salt.

Stir the dry ingredients into the wet ingredients just until the flour is incorporated and the dough is moistened — do not overmix.

Fold in 1/2 cup rolled oats and 1 cup peanut butter and chocolate swirl chips until they are evenly distributed through the dough.

Drop dough by rounded tablespoonfuls onto the prepared cookie sheets, spacing the cookies about 2 inches apart.

Bake in the preheated oven for 10 to 12 minutes, or until the edges of the cookies begin to brown.

Remove the cookies from the oven and let them cool on the cookie sheets for about 5 minutes, then transfer the cookies to wire racks to cool completely.