Preheat the oven to 350°F. Line baking sheets with parchment paper or silicone baking mats.
Cream the butter and sugar on medium-high speed until light and fluffy. Beat in the egg.
Add the flour, hot chocolate mix, cocoa powder and baking powder to the bowl and mix on low speed just until incorporated.
Make round cookie balls about 1 inch in diameter. Place balls onto cookie sheet about 2 inches apart. Snip large marshmallows in half. Press the sticky side of a half marshmallow into the center of chocolate cookie ball, until cookie flattens into a round disc and the marshmallow is partially buried into the center of the disc.
Bake about 10 minutes until cookies are done. Set oven to a low broil. Watching cookies carefully, broil for about 30 seconds to toast marshmallow tops until they turn a deep brown. Let cookies cool a few minutes before eating. If desired, sprinkle a pinch of chocolate shavings on top of each cookie. You can reheat cold cookies in microwave for about 15 seconds each so that marshmallow centers become melted again.
Notes
For the hot cocoa mix, I used Swiss Miss Milk Chocolate.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.