In a large glass bowl, measure out the ground beef, saltines, caramelized onions and egg, salt, fresh thyme, black pepper and red pepper flakes.
Using your hands, mix the ingredients together until well combined.
Form one or two loafs. (I formed one, though I found it would be easier to make two smaller loafs for the browning portion below.)
Turn on the Instant Pot to the Saute setting (Normal) for 10 minutes.
Sear the meatloaf on ALL sides. (If the meat begins sticking, add a little vegetable oil to the pot to assist. I found that there was butter/liquid leftover from the onions that worked just fine.)
When the meatloaf is browned on all sides and the Saute setting is complete, add ½ cup of beef stock.
Put on the lid, and program the Instant Pot to Pressure Cook (Normal) for 18 minutes.
When the pressure cook has completed, depressurize the Instant Pot.
Remove the meatloaf, leaving the pan drippings behind. (This will make the gravy!)