1. Preheat the oven to 350°f / 180°c. Line 2-3 baking sheets with parchment paper (you may have to bake these in several batches depending on how many trays your oven can tolerate).
2. In the bowl of a stand mixer fitted with the paddle attachment, cream the butter and sugar together on high speed until light and fluffy. Add the egg and vanilla and mix to combine. Sift together the flour, baking soda and salt in a small bowl. Add to the mixer, and then add the sprinkles, and mix on low until just combined.
3. Using a 2 Tbsp cookie scoop, scoop balls of dough onto the prepared baking sheets. I like to do 6-8 on each sheet - start with 6 to make sure that they will not join together, and then move to 8 on the next sheet once you know how much they spread.
4. Roll each ball of dough between your hands to form a ball, then roll in the sugar before placing on the baking sheet. Leave any mixture that you are not baking off just yet in the bowl and scoop just before baking.
5. Bake the cookies for 11-12 minutes or until puffy and set around the edges. Remove from the oven and cool on the pan for 10 minutes - the cookies will deflate as they cool. Transfer to a wire rack and allow to cool completely. Repeat the baking process with the remaining cookie dough.

Store cookies in an airtight container at room temperature.