In a large dutch oven or heavy pot, place the meat, onion, garlic cloves, bay leaf and water. Cook for about 50 minutes or until the meat is well cooked through. Strain the cooking broth and reserve. Place the meat back in the pot. The water will reduce during the cooking process, so add more water if needed since we will need 3 cups of the cooking broth to make the sauce.
While the meat is cooking, let's proceed to start making the three peppers sauce. First, we’re going to slightly roast the peppers on a moderately high-heat skillet. This step is a quick one, to avoid burning the peppers. Remember that burned peppers render a bitter taste to your sauce, and we don’t want that flavor in our stew. Roast the peppers by type, since each one has a different texture and thickness. It will be a matter of seconds per side on medium heat; the peppers will change in color and will start to form blisters. After roasting, place them in a medium-size saucepan with 3 cups of water to soak.
Now, toast the sesame seeds until they have a light golden tone. By this time they will start to jump from the skillet. Place in the saucepan with the peppers.
Roast the ¼ piece of onion and 2 unpeeled garlic cloves on the skillet; turn to make sure every side is well roasted. This step will take about 4-6 minutes.
Place roasted peppers, sesame seeds, onion, cumin and garlic in the saucepan. Turn the heat to medium-high and cook for about 5 minutes. Remove from heat and cover the saucepan; allow the ingredients to soften for about 10 more minutes.
To make the sauce, transfer peppers, sesame seeds, garlic and onion in a blender or food processor (discard their cooking water), and add 3 cups of the meat broth previously strained. Blend until you have a fine and smooth sauce.
Pour the sauce over the meat, turn the heat to medium, and slowly fry the sauce with the meat, stirring occasionally, for about 8 minutes. Season with salt and
pepper and reduce heat to keep simmering for about 7 minutes until sauce is slightly reduced and thickened. You can add more cooking broth if you prefer a less thickened texture.