In a small pan, melt 3 tablespoons of unsalted butter over medium heat. Add chopped pecans and toast until fragrant, about 3–4 minutes. Remove from heat and let cool.

In a separate saucepan, melt 2 sticks of unsalted butter over medium-low heat until golden brown, about 5–7 minutes. Let cool slightly.

In a mixing bowl, whisk together 2 cups all-purpose flour, 2 tablespoons cornstarch, 1 teaspoon salt, ½ teaspoon ground cinnamon, and 1 teaspoon baking soda. Set aside.

In a large mixing bowl, whisk the slightly cooled browned butter with 1 cup dark brown sugar, ½ cup granulated sugar, and 2 teaspoons vanilla extract. Add two large eggs and the egg yolk, mixing until smooth.

Gradually add the dry mixture to the wet ingredients on low speed until just combined, about 30 seconds. The dough should be slightly sticky but well-formed.

Gently fold in the cooled, browned pecans using a spatula to ensure they are evenly distributed throughout the mixture.

Cover the bowl and refrigerate the dough for at least 1–2 hours, or up to 24 hours for best flavor and texture.

Preheat the oven to 375°F (190°C) and line baking sheets with parchment paper. Scoop portions of dough onto the sheets, spaced 2 inches apart. Bake for 9–12 minutes until edges are golden and centers remain soft.

Allow cookies to cool on sheets for about 5 minutes, then transfer to a wire rack. Optionally, place a pecan half on top of each cookie before cooling completely.