Combine chopped milk chocolate, natural peanut butter and heavy cream in a large, heatproof bowl. Place the bowl over a large saucepan with 1 inch simmering water and stir occasionally, until the mixture is melted and smooth, about 5 minutes. Remove the bowl from the saucepan, transfer to the refrigerator and then chill until completely cold, about 2 hours.
Whip the mixture with a handheld mixer at medium-high speed until light and fluffy (do not overbeat or mousse will be grainy). Spoon the mixture into 4 bowls and garnish with chopped chocolate-covered peanuts.