Preheat the oven to 375°F (190°C) and line your baking sheets with parchment paper or silicone baking mats.
Using a stand mixer, cream together the butter and sugars until light in color and fluffy in texture. This typically takes about 2 minutes.
¾ cups (167g) salted butter, softened, ¾ cups (185g) brown sugar, ¼ cup (58g) granulated sugar
Add in the eggs, corn syrup and vanilla. Mix until thoroughly combined.
1 egg + 1 egg yolk, 1 Tbsp corn syrup, ½ Tbsp vanilla extract
Next, add the flour, cocoa, hot cocoa mix, cornstarch, baking soda and salt. Mix until your chocolate cookie dough forms. The dough will be soft.
2 cups (304g) all-purpose flour, ½ cup (60g) dutch processed cocoa powder, 1/2 cup (70g) hot cocoa mix, powder only, ½ Tbsp corn starch, 1 tsp baking soda, ½ tsp salt
Scoop out the dough using a #24 cookie scoop and flatten into a disk.
Cut a marshmallow in half and place one half in the center of each disk and pull the dough up around the marshmallow, enclosing it completely. Smooth out the dough until you have a thick puck-like shape.
10 large marshmallows, cut in half
Roll the sides and top of the puck into your sugar/hot cocoa mix, if desired.
sugar/hot cocoa mix (2 Tbsp of each)
Arrange 6 cookies on your prepared baking sheet. Bake for 6-8 mins or until the dough no longer looks glossy and cracks begin to form.
As soon as the cookies come out of the oven press down slightly to help shape the cookies, but do not overdo it, as they will deflate some as the marshmallow cools.
Allow the cookie to cool completely on the cookie sheet.
Once cool, drizzle the tops of each cookie with melted chocolate chips, and add your desired sprinkles/toppings.
1/3 cup (66g) milk chocolate chips, melted
Allow the chocolate to set before serving (you can speed this process up in the refrigerator).
Store in an airtight container on the counter for up to three days. Enjoy!