Preheat the oven to 350°F (175°C) and line two baking sheets with parchment paper or silicone baking mats.

Whisk together the all-purpose flour, baking soda, fine sea salt, and cornstarch in a large bowl; add oats if using.

Cream the softened unsalted butter with granulated sugar and packed light brown sugar until light and fluffy, about 2–3 minutes.

Beat in the eggs one at a time, then add the vanilla extract and mix until combined.

Gradually add the dry mixture to the wet ingredients on low speed, mixing until just combined; add up to 1 tablespoon cold water if dough is too stiff.

Fold in the chocolate chips or chunks and any optional chopped nuts, reserving some chips to press on cookie tops later.

Scoop dough into large rounds (about 2 1/2 tablespoons or a heaping 1/4 cup each) and place them on the prepared baking sheets with at least 2 inches between them; chill scooped dough 10–15 minutes for taller cookies.

If desired, press a few reserved chocolate chips onto each dough ball and sprinkle a pinch of coarse sea salt on top.

Bake for 10–13 minutes until edges are lightly golden and centers remain slightly soft; remove from the oven and allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

When cookies are fully cool, place one or two cookies into each clean, dry cellophane gift bag; add parchment squares between cookies if shipping or stacking to prevent sticking.

If desired, lightly brush a small amount of neutral oil inside the bag top to create a subtle glossy effect, then tie the bag with a length of ribbon threaded through a printed tag, and tuck a small sprig of greenery under the knot.

Arrange packaged cookies in a wooden tray or kraft box with tissue or shredded paper for presentation, making sure not to compress bows or tags.

Store packaged cookies at room temperature for up to 4 days; for longer storage freeze cooled cookies in a single layer and transfer to a freezer-safe container for up to 3 months.