In a large bowl, toss together the lamb, salt, pepper, and flour until the meat is fully coated. Set aside.
Set your pressure cooker to SEAR/SAUTE setting, then add the bacon. Sauté the bacon until cooked, then remove with a slotted spoon to a plate lined with paper towels. Set aside.
Pour a bit of the beef broth into the pot and gently scrape up any brown bits to deglaze the pot.
Add the olive oil to the pot, add the lamb and brown on all sides. Afterward, deglaze the pot with a little more beef broth, if necessary.
Add the garlic and onions, and sauté for 1 to 2 minutes, just until they become soft and fragrant.
Add the carrots, sliced onions, potatoes, thyme, remaining beef broth, Guinness, and sugar to the pot. Add the bay leaf, then stir to combine.
Secure the pressure lid and PRESSURE COOK on HI for 30 minutes. Then allow for natural release (it can take 15 minutes or more for full natural release). Once all of the pressure has been released and the pressure release valve is all the way down, carefully open the lid.
Remember to remove the bay leaf before serving. Top each serving with cooked bacon crumbles.
Notes
Storage: Allow the stew to cool completely, then store leftovers in an airtight container in the refrigerator for up to 5 days. Freeze: Allow the stew to cool completely, then place into airtight freezer-safe bags or containers and freeze for up to 2 months. When ready to serve, thaw the stew in the refrigerator overnight.Reheat: Reheat in a Dutch oven or other large heavy bottom pot until the stew is warmed through. You can add a bit of beef stock to "wake up" the stew and replace any liquid that was lost during freezing or refrigeration.