Preheat oven to 350. Line 2 baking sheets with parchment paper.
In the work bowl of a food processor, pulse chopped pecans until finely ground. Transfer to a medium bowl; add flour, cornstarch, baking powder, and salt, whisking to combine. Set aside.
in the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugars at medium speed until fluffy, 2 to 3 minutes, stopping to scrape sides of bowl. Add egg, oil, and bourbon, beating well. With mixer on low speed, gradually add pecan mixture to butter mixture, beating until combined.
Using a 1 1/2-tablespoon spring-loaded scoop, scoop dough into mounds (about 30 grams each). Using floured hands, roll each mound into a smooth ball, and place 2 inches apart on prepared pans. Using your thumb or the handle of a wooden spoon, gently make an indentation in center of each ball that is deep enough to hold filling.
Bake until edges are lightly golden, 10 to 12 minutes. Remove from oven, and let cool on pans for 2 minutes. Remove from pans, and let cool completely on wire racks. Spoon about 1 teaspoon warm Bourbon Pecan Filling into center of each cookie. Top with pecan halves, if desired.
Bourbon Pecan Filling
In a medium saucepan, stir together all ingredients. Bring to a boil over medium-high heat, stirring frequently. Reduce heat to medium-low; simmer, stirring constantly, until thickened, 3 to 4 minutes. Use immediately.