Preheat your oven to 350°F (175°C) to ensure even baking.
Line your baking sheet with parchment paper for easy cleanup.
In a large mixing bowl, beat together 1 cup of unsalted butter, 1 cup of light brown sugar, and 1 cup of granulated sugar until light and fluffy, about 2-3 minutes.
Add in 3/4 cup of creamy peanut butter and 1 large egg, mixing until well combined and smooth.
In a separate bowl, whisk together 1.5 cups of all-purpose flour and 1 teaspoon of baking soda. Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Using a cookie scoop, drop rounded balls of dough onto the prepared baking sheet, leaving space between each cookie. Bake for 10-12 minutes until edges are lightly golden.
Let the cookies cool on the baking sheet for about 5 minutes before transferring them to a cooling rack.
In a medium bowl, beat together 1/2 cup of melted unsalted butter, 2 cups of confectioners sugar, 1/2 cup of cocoa powder, 1/4 cup of milk, and 1 teaspoon of vanilla extract until smooth and creamy.
Once cooled, frost each cookie with a generous layer of frosting and sprinkle with chocolate jimmies if desired.
Enjoy your delicious Chocolate Frosted Peanut Butter Cookies!