Preheat the oven to 375°F (190°C). Line two baking sheets with parchment paper or silicone mats.
In a large bowl, beat the softened butter, granulated sugar, and brown sugar for about 2 minutes until pale and fluffy.
Add the egg, egg yolk, and vanilla extract. Mix until just combined.
Combine Dry Ingredients
In a separate bowl, whisk together the flour, baking soda, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture, stirring until no streaks of flour remain.
Fold in the milk chocolate chips and toasted pecans using a spatula.
Chill & Bake
Cover the dough and chill in the refrigerator for 30 minutes.
Scoop 2-tablespoon portions of dough onto the prepared sheets, spacing 3 inches apart.
Bake for 9–11 minutes until edges are golden and centers appear slightly underbaked.
Allow cookies to rest on the pan for 5 minutes before transferring to a wire rack to cool completely.
Notes
Chilling the dough for at least 30 minutes helps prevent excessive spreading, yielding thicker, domed cookies.Toasting pecans at 350°F for 5 minutes enhances their depth of flavor and crunchy texture.For an elevated finish, sprinkle flaky sea salt on warm cookies just before serving to balance the sweetness.