Spiced Vanilla Custards with Sweet Potato Streusel

Place 1 tablespoon water in a small bowl; sprinkle gelatin over and set aside. Combine cream, milk, cinnamon, star anise, and 1/4 cup sugar in a medium saucepan and scrape in vanilla seeds; add pod. Bring to a simmer over medium heat. Remove from heat, cover, and let steep 20 minutes.
Uncover infused cream and return to a simmer. Whisk egg yolks with remaining 2 tablespoons sugar in a medium bowl. Whisking constantly, gradually add 1/2 cup warm cream mixture to egg yolks. Reduce heat to medium-low and whisk egg yolk mixture into remaining cream mixture. Cook, stirring constantly, until custard is thick enough to coat a wooden spoon, about 5 minutes. Add gelatin; cook, stirring until dissolved.
Strain custard into a measuring cup. Pour into eight 2 ounces demitasse cups or ramekins. Chill until set, at least 4 hours.
Do ahead: Custards can be made 2 days ahead. Cover and chill.
Preheat oven to 350°. Whisk flour, sugar, salt, and cinnamon in a small bowl. Add butter and work into flour with your fingers until no dry spots remain.
Scatter mixture over a parchmentlined baking sheet, breaking up into large crumbs. Bake, rotating pan halfway through, until streusel is golden brown and crisp, 10–15 minutes. Let cool, then add crumbled sweet potato chips and toss to combine.
Serve custards topped with streusel.
Do ahead: Streusel can be made 1 week ahead. Store airtight at room temperature.