Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large bowl, whisk together melted butter, granulated sugar, and brown sugar until smooth.
Beat in vanilla, egg, and egg yolk until fully combined.
In another bowl, mix flour, baking soda, baking powder, and salt. Gradually fold dry ingredients into wet mixture until just combined.
Fold in chocolate chips. The dough will be slightly sticky but manageable.
Using a cookie scoop or spoon, form 2-tablespoon-sized balls and place 2 inches apart on the baking sheets. Sprinkle a pinch of flaky sea salt on top if desired.
Bake for 10–12 minutes, until edges are golden but centers are soft. Do not overbake.
Cool cookies on baking sheet for 5 minutes, then transfer to a wire rack. Best served slightly warm with melty chocolate.