Preheat and prep: Heat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
Whisk dry ingredients: In a bowl, whisk the gluten-free flour, baking soda, salt, and cinnamon.
Mix wet ingredients: In a larger bowl, whisk the melted butter, brown sugar, and granulated sugar until glossy and smooth, about 1 minute.
Add eggs and vanilla: Whisk in the egg, egg yolk, and vanilla until the mixture looks thick and creamy.
Combine: Add the dry mix to the wet. Stir with a spatula until just combined.
Don’t overmix.
Fold in chocolate: Gently fold in the chocolate chips. The dough should be soft but not greasy.
Portion: Scoop 2-tablespoon mounds onto the sheets, spacing 2 inches apart. For thicker cookies, chill scooped dough 20–30 minutes.
Bake: Bake 10–12 minutes, until edges are set and centers still look slightly underdone.
Finish: Sprinkle a pinch of flaky salt on hot cookies.
Let them cool on the sheet 5–7 minutes, then move to a rack.