Preheat oven to 350°. Grease and prepare a 9x5 inch loaf pan.
In a medium-sized bowl, mix together the flour and salt. Set aside.
In a large bowl of a stand mixer or using a hand mixture, cream the butter and sugar on a medium speed for 3-4 minutes. Once the butter mixture is fluffy, add in the eggs and egg yolk, one at a time, making sure they are fully incorporated. Scrape down the sides as you go. Stir in the vanilla.
Next, add the flour mixture to the butter mixture. Keep the mixer on a low speed and slowly pour the flour mixture in. Once the flour mixture is fully combined, stir in sprinkles. Pour the batter into the prepared pan and set aside.
Make the crumb topping. In a large bowl, combine flour, sugar, and salt. Mix to combine. Using your fingers or a fork, cut in the butter. The crumbs will start to form a sandy-like texture. Once the crumbs start to come together, add in the vanilla and the sprinkles. The crumble should be about pea-sized.
Add the crumbs on top of the batter of the loaf cake. Don't be afraid if it looks a little overstuffed, they will sink into the top of the batter.
Bake in the oven for about 65-75 minutes. The top will look golden brown when done. Allow to cool in the pan for 10 minutes. After ten minutes, run a knife around the outside of the pan to remove the cake. Let it sit on a wire rack until completely cool.