• Preheat the oven to 350ºF with a rack placed in the center.
• Line two baking sheets with parchment paper.

Mix Dry Ingredients:

• In a small bowl, combine the flour, cornstarch, baking soda, and sea salt.
• Set aside.

Cream Sugars and Margarine:

• In the bowl of a stand mixer fitted with the paddle attachment, combine the margarine, light brown sugar, and granulated sugar.
• Mix on medium speed until light and fluffy.

Add Wet Ingredients:

• Add the egg and vanilla to the mixture and mix until combined.

Combine Wet and Dry:

• Gradually add the flour mixture to the wet ingredients and mix on low speed until fully combined.

Fold in Chocolate Chips:

• Remove the bowl from the mixer and, using a rubber spatula, fold in the milk chocolate chips.

Portion Dough:

• Using a ¼-cup scoop, portion the dough into 6 to 8 cookies.
• Place the cookies on the prepared baking sheets, a few inches apart.

Bake:

• Bake one sheet at a time on the center rack for about 15 minutes, until the outside is golden and the inside is still soft.

Cool Cookies:

• Allow the cookies to cool on the baking sheet for 10 minutes before transferring them to a wire rack to cool completely.
• Repeat with the second baking sheet.