Preheat your oven to 350°
Lightly grease and line an 8”x8” baking dish with parchment paper. Set aside for now
In a large bowl, whisk 4 tablespoons of melted butter with 1/2 cup of peanut butter, a large egg and 2 teaspoons of pure vanilla extract until smooth
Add 1/2 cup of brown sugar and 1/3 cup of granulated sugar and whisk until fully combined
Add 1 cup of old fashioned oats, 3/4 cup of all purpose flour, 1 1/2 teaspoon of baking powder and 1/2 teaspoon of salt and mix until just combined
Fold 1/2 cup of chocolate chips, 1/2 cup of M&M’s, 1/4 cup of toffee bits and 1/4 cup of chopped nuts into the dough until evenly distributed
Spread the mixture evenly throughout the prepared baking dish
Bake in a 350° oven for 28-30 minutes or until the edges are golden brown and the center is nicely puffed up
Top with flaky sea salt
Rest for 1 hour before transferring out of the baking dish
Use a sharp knife to cut into slices