
1 ¾ cups (200 g) powdered sugar
3 large egg whites, at room temperature
¼ cup (50 g) granulated sugar
¼ tsp cream of tartar (optional)
½ tsp vanilla extract
Pinch of salt
½ cup (120 g) unsalted butter, softened
1 cup (125 g) powdered sugar
1 tsp vanilla extract or flavorings
Optional: fruit preserves, chocolate ganache, or lemon curd