Gather your cookie ingredients and prepare a baking sheet by lining it with parchment paper. Since the cookie dough will need to chill in the fridge for 30 minutes, there's no need to preheat the oven just yet.

Begin by combining the dry ingredients—flour, baking soda, and salt—in a small bowl. Whisk them together thoroughly, then set the mixture aside.

In a large mixing bowl, place the butter and granulated sugar. Use an electric mixer on high speed to beat them together for 1 minute.

Add the brown sugar and continue mixing until the mixture becomes creamy and fully combined, about 30 seconds.

After the brown sugar is blended in, mix in the egg and vanilla extract.

Now, gradually incorporate the dry mixture into the wet ingredients, mixing until just combined.

After the dough is fully mixed with no visible flour streaks, fold in the chocolate chips.

After mixing in the chocolate chips, use a one-tablespoon measuring spoon to portion out the cookie dough.

Scoop a tablespoon of dough and place it on the prepared baking sheet. Press half of a large marshmallow onto the top of each dough ball.

Take another tablespoon of dough and gently press it on top of each marshmallow, covering it completely.

Refrigerate the dough balls for 30 minutes. Toward the end of this chilling period, preheat your oven to 350°F. Alternatively, you can freeze the dough balls on the baking sheet until firm, then transfer them to bags for storage. Frozen dough remains good for up to 2 months.

To bake the cookies, arrange 6 dough balls on a baking sheet. Sprinkle extra chocolate chips on top of each ball. Bake for 11-13 minutes, or until the edges are golden brown and the centers are gooey and melted, especially if you used large marshmallows.