Rinse the beef tongue with enough water until the water comes out clean.
It usually takes about 3-4 rinses.
Place the beef tongue in the slow cooker.
Add enough water to cover the meat.
Add 1 garlic clove, ½ onion, bay leaf, salt, and pepper to the slow cooker.
Cover and set on low for 6-8 hours, or high 4-6 hours.
Remove the cooked beef tongue from the slow cooker and set aside.
Let cool to touch and peel the outer layer using your hands or tongs.
Remove any fatty areas. (You can also do this part before cooking).
Cut into thin slices.
In a foil-lined sheet pan, add the tomatoes, ½ onion, 1 garlic clove, 1 jalapeño.
Coat with 1 tablespoon olive oil and add salt and pepper.
Broil on high for 8-10 minutes, or until everything is blistered.
Add all the roasted tomatoes, onion, garlic, and jalapeño to a blender.
Blend until smooth.
Taste for salt.
In a large skillet, heat two tablespoons olive oil.
Add the roasted tomato salsa and cook for 2 minutes, stirring occasionally.
Add the cooked beef tongue.
Cover and let simmer for 10 minutes.
Serve with tortillas and Mexican rice.