Preheat oven to 350 degrees. Cream together butter and sugar until light and fluffy; add egg and vanilla. Combine flour and baking soda; add to creamed mixture just until blended. Stir in M&M's Chocolate Baking Bits. Shape dough into 1-inch balls. Place on greased cookie sheets about 2-inches apart. With bottom of a glass dipped in sugar, flatten dough very slightly so as not to crush the baking bits. (NOTE: Very important to keep the balls of dough small and just barely flattened because these SPREAD out a lot.) Bake 10 to 12 minutes or until edges are light golden; let cool 1 minute before removing to wire racks to cool completely. Store in tightly covered containers.