In a skillet, sauté the chopped onion, green bell pepper, and minced garlic cloves in olive oil until softened.

Transfer the sautéed vegetables to the slow cooker.

Add the canned diced green chiles, diced jalapeño (if using), and chopped tomatillos to the slow cooker.

In the same skillet used for sautéing the vegetables, brown the cubed pork until golden brown.

Drain any excess fat and transfer the pork to the slow cooker.

In a mortar or spice grinder, grind together the dried oregano, dried sage, ground cumin, and red pepper flakes.

Add the spice mixture to the slow cooker.

Season with salt and pepper to taste.

Pour in the beer.

Cover and cook on low for 6-8 hours or until the pork is tender and the flavors have melded together.

Serve hot, traditionally in bowls with hot flour tortillas, salsa, and cilantro.

Optional toppings include sour cream, grated cheese, olives, and pickled carrots and jalapeños.

Optionally, for added texture, separate the cooked meat from the broth after cooking, crisp the meat under the broiler, and reduce the sauce in a pan before serving.