1. Preheat the oven to 350°F (175°C) and line two baking sheets with parchment paper or silicone baking mats.

2. In a large mixing bowl, beat the softened butter, light brown sugar, and granulated sugar together until light, creamy, and slightly fluffy, about 2–3 minutes.

3. Add the eggs one at a time, mixing just until incorporated, then blend in the vanilla extract and scrape down the sides of the bowl.

4. In a separate bowl, whisk together the all purpose flour, baking soda, salt, and cornstarch until well combined.

5. Add the dry ingredients to the wet ingredients in two additions, mixing on low speed or by hand just until no streaks of flour remain.

6. Fold in the semi sweet chocolate chips and peanut butter baking chips with a spatula until they are evenly distributed through the dough.

7. Scoop the dough into balls about 1 1/2 to 2 tablespoons each and place them on the prepared baking sheets, leaving space between each cookie to allow for spreading.

8. Bake for 9–11 minutes, or until the edges look set and lightly golden while the centers still appear soft and slightly underbaked.

9. Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely before serving.