Step 1

Add all chipotle sauce ingredients to a food processor or blender, and process until smooth. Set aside.

Step 2

Trim visible large sections of fat from roast, then cut roast into 6-8 large pieces. Season beef with 1/2 tsp each salt and pepper.

Step 3

Add vegetable oil to Instant Pot and select "Saute". When hot, add beef and cook for a minute or so on each side, until browned. Depending on the size of your beef, you may need to do this in batches.

Step 4

Remove browned beef to a plate and add onion. Saute for 2-3 minutes, until soft.

Step 5

Add in 1 cup beef broth and scrape the bottom of the pot with a wooden spoon to remove any browned bits. Add in tomato paste, green chiles and bay leaves.

Step 6

Press "Cancel - or Keep Warm/Cancel". Return browned beef to the pot and pour pureed chipotle sauce over the top. Top with both halves of the lime.

Step 7

Close lid securely and make sure the valve is set to "sealing". Select "Manual" or "Pressure Cook" and adjust the +/- button until it reads 60 minutes.

Step 8

When finished cooking, carefully turn the valve to "venting" for a quick pressure release. When the steam has all escaped, and the pin has dropped, remove the lid and discard bay leaves.

Step 9

Remove beef pieces to a large bowl and shred, discarding any purely fat parts.

Step 10

Toss shredded beef with as much of the cooking liquid as you'd like.

Step 11

In a small bowl, stir together 2 Tbsp cornstarch with 3 Tbsp water until smooth. Pour this mixture into the pot with the sauce and select "saute".

Step 12

Cook for several minutes, stirring often, until thickened to your tastes.

Step 13

Toss shredded beef with as much of the thickened sauce as you'd like.

Step 14

Line a baking sheet with foil, and preheat broiler to high, adjusting oven rack to the upper third position.

Step 15

Spread shredded beef into an even layer, then broil several minutes. Stir. Continue broiling and stirring until crisped and charred to your liking.