In a large mixing bowl, cream the butter, shortening, and sugar until smooth.
Add the egg and vanilla. Mix together.
Sift the flour and baking soda.
Gradually add the baking soda and flour to the bowl with the butter mixture.
(Little by little, or the flour will go everywhere).
Wrap the dough in plastic wrap.
Place in the fridge for 1 hour to chill.
Preheat the oven to 350 degrees F.
Pour sprinkles into a plate and set aside.
Cut the dough in half.
Take out two pieces of parchment paper.
Roll half the dough between the parchment papers and cut-out cookies with a cookie cutter.
Gently remove the cookie from the rest of the dough.
Press it lightly into the sprinkles.
Then place it on the baking sheet.
Repeat with all of the cookies and other half of the cookie dough.
Bake for 11-13 minutes.
Remove from the oven and let them cool completely.