Yield: Just shy of 3 shakes in the 12-ounce glasses shown; 4 to 5 shakes in the 8-ounce glasses we found to be a better portion size later
1 (10-ounce, 283-gram) bag large marshmallows, divided
1/2 cup milk
Seeds scraped from 1/2 a small vanilla bean or 1 teaspoon vanilla extract
2 cups vanilla ice cream
2 tablespoons sour cream, plain yogurt or crème fraîche
1/4 cup heavy cream beaten to soft peaks with 1 teaspoon powdered sugar, for a whipped cream garnish (optional)
Place your glasses in the freezer. Heat your broiler. Line a baking sheet with foil and coat it lightly with a nonstick spray. Set aside the number of marshmallows you’ll want for garnishes (estimate 1 to 2 per shake) and spread the rest on the tray. Broil, keeping a close watch as the marshmallows will take on color very quickly, for 1 to 2 minutes, until they’re the color you like. Don’t be afraid of a little char; it really enhances the shake. Cool the tray in the freezer for 5 minutes, until marshmallows are no longer warm, then transfer broiled marshmallows to your blender. Blend with milk until as pureed as you can get them, then pause to individually toast marshmallows for garnish over a gas flame or back under your broiler for a moment. This ensures that they’re warm when they hit the glass. Add vanilla bean or extract, ice cream and sour cream to the marshmallow mix in the blender, and blend until thick and smooth. Pour into chilled glasses, finish with a dollop of whipped cream, if using, and a warm marshmallow. Slurp through a straw; repeat again very soon.