Melt butter in a medium pot over medium heat, then add peanut butter and butterscotch chips. Heat until peanut butter and butterscotch chips are melted.

Add marshmallows and continue to heat and stir until marshmallows are melted and mixture is well blended.

Place oat cereal in a large bowl, then pour liquid mixture over the top. Mix well with a wooden spoon, then press into a 7x11 pan lined with parchment paper. Press with the back of your spoon or your slightly dampened hand. Set aside.

Chocolate top: place chocolate chips and butter in a microwave safe bowl and microwave for 20 seconds, stir until chocolate is smooth.

Working quickly, pour melted chocolate over the oat squares and smooth out with rubber spatula. Place in the fridge for about 10 minutes until chocolate is beginning to set, then remove and sprinkle with salt. Return to fridge and allow chocolate to fully set, then cut into squares.