Combine cocoa, flour, baking soda and salt in medium bowl.

Melt I Can't Believe It's Not Butter in a large saucepan over medium heat; cool slightly.

In another bowl, add the I Can't Believe It's Not Butter and the sugar, and whisk until smooth.

Whisk in the eggs, one at a time until well-blended.

Stir in the vanilla and add the flour mixture until well-combined.

Wrap the dough in plastic wrap; refrigerate 2 hours.

Preheat oven to 350 degrees Fahrenheit.

Shape dough into 1 inch balls and place onto greased cookie sheets.

Place the remaining ½ cup of sugar in a shallow bowl and roll the balls in sugar.

Bake 12 minutes and then let the cookies stand for about 5 minutes before transferring them to wire racks to cool completely.

Spread frosting on the flat side of one cookie and then top with another cookie to make a sandwich. Place sprinkles on a plate and roll the outside edges of the cookie in the sprinkles.