For the Cake:

1. Preheat oven to 325°F (170°C).
2. Spray a 9×5-inch loaf pan with baking spray; line with parchment paper, letting excess extend over sides of pan. Spray pan again.
3. In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugar at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl.
4. Add eggs and egg yolk, one at a time, beating well after each addition. Beat in vanilla.
5. In a medium bowl, whisk together flour and salt. Reduce mixer speed to low, and gradually add flour mixture to butter mixture, beating just until combined.
6. Stir in sprinkles. Pour batter into prepared pan. Sprinkle with cake crumb topping. You might not need all the topping (I used about half ) but you can save the rest for up to 3 days in your refrigerator. It’s great over ice cream!
7. Bake until golden brown and a wooden pick inserted in center comes out clean, about 1 hour and 10 minutes. Let cool in the pan for 10 minutes.
8. Using excess parchment as handles, remove the cake from pan, and let cool completely on a wire rack. Store in an airtight container for up to 3 days.

For the Topping:

1. In a large bowl, whisk together flour, sugar, and salt.
2. Using your fingers, work in cold butter until mixture has a sandy texture.
3. Add sprinkles and vanilla, and mix with your fingers until small pebble-size crumbs remain.