I added almost 3/4 cups of chocolate chips and marshmallow bits to my dough (vs. the original 1/2 cups) and found it enhanced the flavor without being too lumpy.
For smoother (but less hot chocolatey-flavored) cookies, remove the mini chocolate chips and marshmallow bits from the recipe.
I rolled my cookies to a 1/4" thickness and they cooked perfectly at 8 minutes.
The marshmallow bits may melt a bit during baking; for the few that left holes, I just replaced them while the cookies were still warm after baking.
HOT CHOCOLATE ROLLOUT COOKIES
INGREDIENTS
1 cup (2 sticks) unsalted butter, at room temperature
1/2 cup sugar
1/2 cup light brown sugar
1 egg
3 packets powdered hot chocolate mix
1 1/2 teaspoons pure vanilla extract
3 cups all-purpose flour
1/2 - 3/4 cup miniature milk chocolate chips (optional)
1/2 - 3/4 cup marshmallow bits (optional)
DIRECTIONS
In the bowl of an electric mixer fitted with the paddle attachment, mix the butter, sugar, and brown sugar together until smooth.
Add the egg, vanilla extract, and hot chocolate powder and mix until well incorporated.
Add flour and mix until well incorporated (dough will wrap around the paddle attachment).
If desired, stir in the miniature chocolate chips and marshmallow bits.
Roll dough between two pieces of parchment paper to your desired thickness and chill for minimum of 30 minutes.
When ready to bake, preheat oven to 375°F.
Roll the dough 1/4" thick on a lightly floured surface or between two sheets of parchment paper and cut into desired shapes.
Bake 7-9 minutes. Remove and gently smooth tops using a metal spatula. Let cool for 10 minutes before transferring to wire racks.