1 pound strawberries, hulled, halved
3 tablespoons raw sugar
1 frozen banana
1/2 cup buttermilk
3 tablespoons tahini
Crushed toasted sesame seeds (for serving; optional)
Preheat oven to 400°. Toss strawberries with sugar and a pinch of salt on a parchment-lined rimmed baking sheet. Let sit, tossing occasionally, until sugar dissolves, about 5 minutes. Roast, tossing halfway through, until strawberries are soft and release their juices, 20–25 minutes. Let cool.
Transfer three-quarters of strawberries to a blender. Add banana, buttermilk, tahini, and 1 cup ice; blend until smooth. Using a metal spoon, smash remaining strawberries to a jammy consistency.
Divide smoothies and strawberries among glasses and top with sesame seeds, if using.