How to Make It
Place cream in a large chilled bowl; beat with an electric mixer until stiff peaks form, 2 to 3 minutes. Gently fold in condensed milk until fully incorporated (do not overmix). Cover bowl with plastic wrap so that plastic rests on surface of mixture. Freeze until firm, 8 to 10 hours.
Preheat oven to 325°F. Line a rimmed baking sheet with parchment paper. Spread rice flour in a thin layer on prepared baking sheet. Toast in preheated oven until flour smells nutty and is sandy in color, 12 to 14 minutes. Set aside. On a second parchment-lined rimmed baking sheet, spread sesame seeds in a thin, even layer, and toast until fragrant, 6 to 8 minutes. Let stand until cool.
Place 1/3 cup toasted sesame seeds in the bowl of a food processor. Pulse until seeds are coarsely ground, about 8 times.
Sift powdered milk, sugar, and toasted rice flour into a large bowl. Add ground sesame seeds and remaining toasted sesame seeds to bowl. Gently stir in melted butter. Let cool; transfer to an airtight container.
To serve, spoon 3 small scoops of ice cream into a bowl, and sprinkle liberally with sesame mixture.