Preheat your oven to 350 degrees and line two baking sheets with either parchment paper or silicone baking mats. Set aside.
In a large bowl, add the melted (& cooled) butter, white sugar, and brown sugar and mix on medium until combined. (I used my hand mixer - stand mixer will def work, too)
Add in the vanilla and egg and beat until just combined.
Add in the flour, baking soda, and salt and mix until a dough forms.
Pour in the peanut butter chips and mini chocolate chips and stir with a spoon until distributed.
Use a medium cookie scoop to scoop out 12 to a pan. (My batch made 17 cookies)
Bake for 10-12 minutes or until pale and puffy and edges just start to brown.
Remove from oven and allow to cool for 10 minutes before removing from the pan to finish cooling.