In a large mixing bowl or the bowl of a stand mixer fitted with a paddle, beat the softened unsalted butter, granulated sugar, and light brown sugar on medium speed until light and fluffy, about 2–3 minutes.

Add eggs and vanilla

Add the eggs one at a time, mixing well after each addition. Add the vanilla extract and mix until incorporated.

Incorporate wet banana and peanut butter

Stir the mashed ripe banana and 1/2 cup creamy peanut butter into the butter-sugar-egg mixture until evenly distributed. The batter will be slightly softer and fragrant from the banana and peanut butter.

Combine with dry ingredients

With the mixer on low speed, gradually add the flour mixture and mix just until combined. Do not overmix.

Monkey mix-ins (banana + peanut butter components)

Add oats, peanuts, and chips

Fold in the quick oats, chopped roasted peanuts, and milk chocolate chips with a spatula until evenly distributed throughout the dough.

Portion cookies

Using a medium cookie scoop (about 2 tablespoons) or a tablespoon, portion dough into rounded balls and place them 2 inches apart on the prepared baking sheets. Slightly flatten each ball with the back of the scoop or your palm — these cookies spread modestly.

Bake

Bake in the preheated oven for 10–12 minutes, rotating the sheets halfway through if needed. Cookies should be golden at the edges and still slightly soft in the center.

Cool

Remove baking sheets from the oven and allow cookies to cool on the sheet for 5 minutes, then transfer cookies to a wire rack to cool completely.

Optional finishing

Peanut butter drizzle and salt

If using, warm the additional 2 tablespoons of peanut butter (15–20 seconds in the microwave) until pourable. Drizzle over cooled cookies and sprinkle with a tiny pinch of coarse sea salt on each cookie. Allow peanut butter drizzle to set for a few minutes before serving.

Storage

Store cooled cookies in an airtight container at room temperature for up to 3 days or freeze for up to 3 months. If frozen, thaw at room temperature.