Preheat your oven to 350°F (175°C). Line your baking sheets with parchment paper for easy cleanup and to help your cookies bake evenly.

Mix the dry ingredients: In a large mixing bowl, whisk together the flour, baking soda, and baking powder until fully combined. This will help ensure an even rise for your cookies.

Cream the wet ingredients: In another bowl, combine the softened butter, granulated sugar, brown sugar, vanilla extract, and the egg. Use a hand mixer or stand mixer to beat the ingredients together until the mixture is light and fluffy. This should take about 2 minutes.

Combine wet and dry ingredients: Pour the wet ingredients into the dry ingredients and mix until just combined. Be careful not to overmix; doing so can result in tough cookies. The dough should be slightly soft and sticky.

Add chocolate: Stir in the chocolate chips (or chopped chocolate) until evenly distributed throughout the dough. The chocolate will start to melt as you mix, creating a few pockets of delicious gooey chocolate.

Chill the dough (optional): If you have the time, cover the dough with plastic wrap and chill it in the fridge for about 1 hour. Chilling the dough helps the cookies maintain their shape while baking and allows the flavors to meld together. If you’re in a rush, you can skip this step, but it’s highly recommended for the best results.

Scoop the dough: Use a tablespoon or a cookie scoop to form 18-20 dough balls. Place them about 2 inches apart on the prepared baking sheets.

Add marshmallows: Cut your mini marshmallows into small pieces (about 2-3 pieces per cookie) and gently press them into the top of each cookie dough ball. The marshmallows will melt and puff up as they bake, creating that gooey marshmallow center.

Sprinkle with sea salt: Before placing the cookies in the oven, sprinkle a pinch of sea salt over each one. This small touch enhances the sweetness of the chocolate and marshmallow, giving the cookies a touch of sophistication.

Bake the cookies: Bake for 10-12 minutes, or until the edges are golden brown but the centers are still soft. Remember, don’t overbake if you want chewy, gooey cookies! They will continue to cook on the baking sheet after you take them out of the oven.

Cool and enjoy: Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack. This allows them to set and prevents them from falling apart while they’re still too soft.