Use electric mixer fit with paddle attachment to beat butter, sugar, and brown butter until lightened and fluffy, about 2 minutes.

Mix in peanut butter and vanilla until well combined. Add eggs, one at a time, scraping down sides as needed.

In a medium sized bowl, whisk together flour, cornstarch, baking soda, and salt. Add to butter mixture and mix until combined.

Stir in oats, chocolate chunks, and chocolate chips until evenly dispersed. Place dough in refrigerator for 1 hour.

Preheat oven to 350 degrees. Use ungreased baking sheet, or baking sheet lined with silicone baking mat or parchment paper.

Form dough into ~1 tablespoon sized balls. Place on baking sheet at least 2 inches apart.

Bake for 10-12 minutes, or until golden brown.