Begin by melting 1/2 cup of semi-sweet chocolate chips in a heat-proof bowl placed over simmering water or in the microwave at 30-second intervals, stirring until smooth.

In a large saucepan, over medium heat, add 1 cup of unsalted butter. Continuously stir the butter as it melts until it turns a light amber color and develops tiny brown specks, which will take about 5-7 minutes.

Reduce the heat to low, and add in the majority of the mini marshmallows, reserving 1 cup for later. Stir the mixture continuously until the marshmallows are fully melted and combined with the brown butter, about 2-3 minutes.

Once the marshmallows are melted, remove the saucepan from heat. Add 1 teaspoon of vanilla extract and a pinch of salt, then gently fold in 6 cups of Rice Krispies and the reserved marshmallows.

Prepare a 9x9-inch baking dish by greasing it lightly or lining it with parchment paper. Pour the Rice Krispie mixture into the dish, pressing it into an even layer for about 1-2 minutes.

Melt the remaining 1/2 cup of semi-sweet chocolate chips and drizzle over the top of the Rice Krispie treats. Sprinkle the mini M&Ms over the drizzle.

Allow the treats to set at room temperature for about 1 hour, slice them into squares, and enjoy!