Add butter, pecans, brown sugar, corn syrup, salt and beaten eggs to a medium non-stick pan. Cook over medium-high heat until it becomes thickened. Do not overcook, you want it the same consistency as pudding. Remove from heat and set aside.
Preheat the oven to 375 degrees F. Line baking sheets with parchment paper.
In a stand mixer or large bowl using a hand mixer, blend the butter, brown sugar, granulated sugar, vanilla and eggs. In a medium bowl, stir together the flour, cocoa, baking soda and salt. Gradually add the flour mixture into the butter mixture and blend until combined.
Drop the dough by tablespoonful onto the prepared baking sheets, 12 cookies per sheet, and bake 8 minutes.
Remove from oven and top cookies with approximately 1 tablespoon of pecan cookie filling on the center of each cookie. Place back in oven and cook for another 4 minutes. Remove from oven and allow to cool on baking sheet. Repeat with remaining doing and pecan cookie filling.