Preheat oven to 350°F.

For the cake:

In the bowl of a stand mixer (or use a hand-held mixer), beat together the melted butter, bourbon, coffee, eggs, sour cream, and sugar until combined. Add the flour, cocoa powder, baking soda, and salt. Mix until smooth and no lumps remain in the batter. Spread batter into a cookie sheet lined with parchment paper.

Bake for 1 5 minutes. Remove and allow cake to completely cool.

For the filling:

In a medium saucepan, mix together cornstarch and brown sugar. Beat together the egg yolks, water, and a pinch of salt. Add the egg yolk mixture to the cornstarch mixture along with the chopped pecans. Simmer on medium heat, stirring constantly, until thickened. Add bourbon and boil for 1 minute, still stirring constantly. Remove from heat; stir in the butter. Allow mixture to cool.

For the frosting:

Using an electric mixer, cream together cream cheese and butter until light and fluffy.

Add in brown sugar and vanilla; cream for 3–4 minutes. Add powdered sugar 1 cup at a time, until desired consistency is reached. For a thicker frosting, add additional powdered sugar.

Assemble the jars by cutting the cake using a round cookie cutter. Place a cake round into bottom of each jar. Next, add 2 heaping tablespoons of filling followed by another cake round. Top with frosting and garnish with a pecan.