Line a 9 x 9-inch baking dish with parchment paper. Set aside. 

In a large pot, combine the chocolate chips and sweetened condensed milk. Heat over low-medium, stirring continuously. 

After chocolate is completely melted and mixture is smooth, add the butter and salt. Stir to combine. Then remove from heat. Add the bourbon, and stir until completely mixed. 

Carefully pour the fudge into prepared baking dish, and use a spatula to smooth it into an even layer. Set aside.

In a medium pot, add the sugar, water, and lemon juice, Give it a gentle stir (just to combine ingredients), taking care not to splash any on the side of the pan. DO NOT STIR AGAIN DURING THE BOILING PROCESS. 

Bring the ingredients to a boil over low-medium heat, and continue to boil until the sugar becomes golden brown in color. Carefully add the heavy cream and butter. The mixture will bubble a lot, so take care not to let it boil over. 

Remove from heat and stir until the heavy cream and butter are combined, and the caramel is no longer boiling. 

Immediately pour the caramel over the fudge, and place it in the refrigerator for 4 hours. After the fudge sets, remove it from the pan, and cut into squares. Serve immediately, or store in a sealed container in the refrigerator for up to 5 days.