Preheat oven to 375 F. Mix your softened butter, white sugar, and brown sugar in a mixing bowl.
Mix with a stand mixer or fork until it's evenly incorporated.
Add the egg, baking soda, salt, and vanilla extract; mix until the egg is evenly incorporated.
Begin stirring in your flour, about 1/2 cup at a time. If it looks too "sticky" add flour at a table spoon at a time until your dough holds it's shape when you take a spoonful. Optionally, you can put this in the fridge for 20 minutes so it holds better shape.
Place 8 - liberally rounded tablespoon sized cookie dough balls on a cookie sheet about 1-2 inches apart. Top them with m&ms.
Cooke for 8-12 minutes, until the center is no longer doughy. For my oven 10 minutes works. Let them sit for about 20 minutes so they are no longer warm to the touch.
To make them into Ice Cream Cookie Sandwiches, take a ice scream scoopful of vanilla ice cream, and place on the bottom side of one cookie. Carefully, but firmly press the other cookie on top.
Add sprinkles all over the ice cream, then wrap in saran wrap and freeze over night. Then they're ready to eat! Enjoy!