Heat oven to 350°F.
Combine 3/4 cup butter and sugar in bowl. Beat at medium speed, scraping bowl often, until creamy. Add eggs, 1/4 cup milk and vanilla. Continue beating until well mixed. Reduce speed to low; add flour, cocoa mix and baking soda. Beat until well mixed.
Drop dough by rounded teaspoonfuls onto ungreased cookie sheets. Bake 8-9 minutes or until set. Remove from oven; top each cookie with marshmallow half, cut-side down. Continue baking for 1-2 minutes until marshmallow just begins to puff. Immediately remove cookies to cooling racks. Cool completely.
Place powdered sugar into bowl; set aside. Combine all remaining glaze ingredients in 1-quart saucepan. Cook over medium heat until mixture comes to a boil; boil 1 minute. Remove from heat; cool 5 minutes. Pour mixture over powdered sugar in bowl. Beat at medium speed until creamy.
Immediately spoon glaze over cooled cookies. Store between sheets of waxed paper in a loosely covered container.
- Cool and clean cookie sheets between batches. The cookies may stick slightly to the sheet.
- If glaze gets too thick to drizzle, beat in 1 additional teaspoon of milk.