In a large bowl, whisk together flour, sugar, and salt. Using your fingers, work in cold butter until mixture has a sandy texture. Add sprinkles and vanilla, and mix with your fingers until small pebble-size crumbs remain. Refrigerate for up to 3 days.
Recipe by Bake from Scratch at https://www.bakefromscratch.com/rainbow-sprinkle-bread-birthday-crumb-topping/