Preheat oven to 300⁰F.

Combine dry ingredients and sprinkles in the bowl of your stand mixer. When well mixed, add oil and vanilla. Mix again. The ingredients should start forming in to "clusters".

Cover a baking sheet with parchment paper or a non-stick baking mat. Spread the clusters on the baking sheet. Bake for 20 minutes. If clusters are baking together, you can break them apart a few times during the baking process.

Remove crumbs from oven and let cool.

Cream butter, sugar, and corn syrup in a stand mixer for 3 minutes. Add the eggs and vanilla and beat for 8 more minutes. This long creaming process is part of what makes these cookies so amazing. Do not cut down on the time!

Scrape the sides of the bowl. Add the dry ingredients and the sprinkles. Mix on low until the ingredients come together. Do not over-mix. (That would negate the creaming process we just did.)

Add the cooled birthday crumbs to the dough and mix just until incorporated.

Scoop the dough onto parchment-covered sheet pans and pat the tops down. The recipe calls for using 1/3 cup dough for cookie. This is a pretty large cookie, but I highly recommend it for it several reasons: 1) Everybody loves and wants a giant cookie, 2) They come out amazingly soft and wonderful at this size. You can make smaller cookies if you want, but just make sure to cut down the baking time accordingly.

Refrigerate cookie dough disks for at least an hour before baking. Toward the end of the chilling, preheat your oven to 350⁰F.

Arrange your chilled cookie dough disks about 4 inches apart if you are making the ⅓ cup size cookies. Bake the cookies for about 18-20 minutes or until they puff and spread. The middle of the cookies will be less golden-brown than the outside of the cookies, but they should not be doughy pale.

Cool on the sheet before storing in containers. They will keep at room temp for about 5 days.