Beat together butter and sugar using an electric mixer until combined. Blend in vanilla. Add cake mix, flour, salt, and vanilla and mix thoroughly. Add 3 Tablespoons of milk or more if needed to make a dough consistency. Mix in sprinkles by hand. Roll dough into one inch balls and place on a parchment or wax paper lined cookie sheet. Chill balls in the refrigerator for 15 minutes to firm up.