Set instant pot to saute mode. Add roast with onions and sear all sides of roast. 

Turn off saute mode. Add 1/2 cup broth. Place lid on instant pot and lock. Place pressure valve to close. Set to high pressure for 1 hour and 15 minutes.

Once instant pot stops counting quick release the pressure. 

Open lid. Add in carrots, celery, allspice, peppercorns, and bay leaves. Replace lid on top. Lock lid. Turn pressure valve to close. Set to high pressure for 15 minutes.

Once instant pot stops counting quick release pressure. 

Remove roast to cutting board. 

With an immersion blender or using a blender blend all of the vegetables and herbs. 

Add in lemon juice, half and half, 1/2 cup chicken broth, and wondra flour to vegetable gravy. Set to saute mode. Cook stirring often until sauce is thickened. 

Serve topped over sliced roast with dumplings. May also be served with noodles or rice.