Preheat oven to 350°F (175°C) and line two baking sheets with parchment paper. In a medium bowl, whisk together the flour, baking soda, and salt.

In a large bowl, stir together the melted butter, brown sugar, and granulated sugar until smooth. Add the egg and vanilla and stir vigorously until combined.

Add the dry ingredients to the wet mixture and fold until just combined, then fold in the milk chocolate chips.

Drop 1 1/2 tablespoon mounds of dough onto the prepared sheets about 2 inches apart. Bake for 10 to 12 minutes, until edges are golden. Let cookies cool on the sheet for 5 minutes, then transfer to a wire rack.