In a small bowl, mix together the flour, baking soda, and salt. Set aside.
In a large bowl, cream the softened butter, both sugars, and vanilla extract, by beating on medium-high speed with an electric stand mixer or hand mixer until creamy.
Add the eggs, one at a time, and beat well after each addition.
Add the dry ingredients into the butter mixture and mix on low speed until just incorporated. A small amount of flour should still be visible.
Fold the chocolate chunks into the dough using a large spatula or spoon. Refrigerate for at least an hour, or overnight.
When ready to bake, preheat the oven to 350°F (177°C). Use a 2-tablespoon scoop to portion onto a baking sheet, 3-inches apart.
Bake for 6-7 minutes, until the cookies have flattened but are not yet finished baking. Remove the tray from the oven and gently press 3-5 marshmallows into each cookie. Return tray to the oven for an additional 2-3 minutes, until the edges of the cookies start to brown and the marshmallows are gooey.
Cool for 5 minutes on the baking sheet, then transfer to a cooling rack and cool completely.
For an extra chocolatey flavor, add an additional ½ cup of chocolate chips.
To get the toasty look on the marshmallow tops, turn the oven onto broil for the last minute of cooking, and place the cookie sheet on the top rack of the oven. Watch carefully, to ensure your cookies do not burn.
Store in an airtight container at room temperature for up to a week.