In the bowl of a stand mixer with paddle attachment, beat butter and sugar together until fluffy.
Lower speed of mixer and add flour, baking soda and salt, and mix until combined.
Add sprinkles and give a final stir.
Let cool completely.
In the bowl of a stand mixer, combine butter and powdered sugar.
Add vanilla and and salt and mix until well combined. Slowly mix in heavy cream, adjusting amount as needed.