In a large greased preheated skillet over medium high heat, brown off meatballs, a few at a time, working in batches; reserve browned meatballs and keep warm.
Using the same skillet, add bourbon to deglaze the pan; stir to bring up any browned bits attached to the bottom of the skillet. Add ketchup, brown sugar, lemon juice, Worcestershire sauce, and red pepper flakes, stirring to combine.
When sauce is nicely warmed, add reserved meatballs and lower heat; let meatballs simmer in skillet for 20-30 minutes, until hot throughout and sauce has thickened slightly. Serve meatballs garnished with sliced scallions, if desired.
Instant Pot Method
Preheat pressure cooker pot using browning setting; spray with nonstick spray or add a bit of oil to the pot, then add meatballs, a few at a time, working in batches, browning off meatballs on all sides. Reserve browned meatballs and keep warm.
Add bourbon to the pot to deglaze, stirring up any browned bits attached to the bottom of the pressure cooker pot. Add ketchup, brown sugar, lemon juice, Worcestershire sauce, and red pepper flakes, stirring to combine. When sauce is warmed, add reserved meatballs and simmer for just a couple of minutes in the sauce, until hot throughout, and sauce has thickened a bit. Serve meatballs garnished with sliced scallions, if desired.