Impossibly Creamy Pumpkin Mousse Is the No-Bake Dessert of Fall

Place the remaining 6 ounces cold mascarpone cheese (generous 3/4 cup), remaining 1/2 cup packed brown sugar, 1 cup pumpkin purée, 1 1/2 teaspoons pumpkin pie spice, and 1/4 teaspoon kosher salt in the now-empty bowl (or large bowl if using an electric hand mixer or whisking by hand). Beat with the whisk attachment on medium speed, scraping the bowl down about halfway through with a flexible spatula, until smooth, 1 to 1 1/2 minutes total. Scrape down the bowl again.