Preheat your oven to 350 degrees.
Cream butter and brown sugar together well until combined.
Add in egg and vanilla and continue mixing, then mix in instant vanilla pudding, baking soda and salt.
Add in flour and continue mixing until combined.
Stir in M&M's.
Using a cookie scoop, scoop dough onto greased pan spacing them about 2 inches apart. Bake for 10-11 minutes or until golden.