In a small skillet over medium heat, melt 3 tablespoons of unsalted butter. Add the finely chopped pecan halves and toast them for about 3–5 minutes until they are fragrant and lightly golden. Remove from heat and let the pecans cool. In a separate saucepan, melt the remaining two sticks of unsalted butter until browned, approximately 5–7 minutes; then set aside to cool slightly.

In a medium bowl, whisk together 2 1/2 cups of all-purpose flour, 1 tablespoon of cornstarch, 3/4 teaspoon salt, 1 teaspoon of baking soda, and the optional 1/2 teaspoon ground cinnamon. Mix until well combined.

In a large mixing bowl, combine the slightly cooled browned butter with 1 cup of dark brown sugar and 1/2 cup of granulated sugar. Whisk thoroughly until smooth and creamy, then add in 1 tablespoon of vanilla extract, the 2 large eggs, and the egg yolk, mixing well.

Gradually add the dry ingredients to the wet mixture, using a spatula or wooden spoon to combine gently. Mix until just combined.

Gently fold the cooled browned pecans into the cookie dough, ensuring they are evenly distributed.

Cover the dough tightly with plastic wrap or place it in an airtight container. Refrigerate for a minimum of 1–2 hours, or up to 24 hours.

Preheat your oven to 375°F (190°C). Line your baking sheets with parchment paper. Use a cookie scoop or tablespoon to portion out chilled dough onto the sheets, spacing them about 2 inches apart. Bake for 9–12 minutes.

Allow the cookies to cool on the baking sheet for about 5 minutes to set, then transfer them to a wire rack to cool completely. Optionally, decorate each cookie with a pecan half.