Preheat oven to 375 degrees F.
Cube butter into tablespoon sized pieces.
Place a skillet over medium-low heat and whisk in butter cubes.
Whisk continuously for about three and a half - five minutes, or until the butter starts to smell like caramel and there are brown bits forming in the bottom of the pan.
Remove from heat and continue to whisk for thirty more seconds.
Remove from pan into a bowl and aside to cool.
Once the butter has cooled (does not need to re-solidify, just cool down), cream browned butter and both sugars until smooth.
Add in peanut butter, egg, and vanilla and mix until the egg is well incorporated.
You may need to stop and scrap down the bowl a few times.
Slowly add the baking soda, salt, and flour until combined.
Lastly, add in chocolate chips and mix well.
Using a cookie scoop (1.5 T), scoop cookie dough onto a prepared baking sheet (greased or lined with a silpat mat).
Gently press down on the dough to flatten and place 8 mini marshmallows on top of the cookie dough. Top with another scoop of cookie dough and gently squish together until it forms one cookie. *See the notes below for more detailed instructions on how I stuffed the cookies.
Bake for 8-15 minutes or until the bottom is lightly golden (baking time varies depending on if you're stuffing the cookies or not).
Remove from oven and let set for 5-10 minutes.
Remove from the baking sheet and transfer the cookies onto a cooling rack.
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