First, let’s make the birthday cake crumb. Preheat the oven to 300.
Mix all the dry ingredients and sprinkles together.
Add in the melted butter and clear vanilla extract and mix until a crumbly texture comes together.
Spread out on a cookie sheet and bake for 15 minutes, stirring the crumbs at the halfway point. Allow to cool and set aside.
Now for the cookies: Preheat the oven to 350.
Add the butter and sugar to a bowl (or mixer on slow) and begin to work the butter into the sugar until creamy.
Next, add in the egg yolks and clear vanilla extract and mix slowly, but well, until creamy and smooth.
Lastly, add in the flour, remaining dry ingredients, and sprinkles and mix until the dough comes together.
Line a cookie sheet with parchment paper. Using a big cookie scoop (3 tbsp), scoop out the dough and place on the cookie sheet, leaving a good amount of space in between (I do 5 at a time).
Bake for 13-14 minutes until just lightly golden. Allow to cool completely.
Lastly, for the frosting. By hand or slowly in a mixer, cream the butter until just smooth.
Then, add in the powdered sugar and clear vanilla and cream together until just smooth, creamy and fluffy.
To assemble: Once the cookies are totally cooled, pipe on a generous amount of frosting to the top of each cookies, then sprinkle on a little bit of the crumble to each cookie. Enjoy!