Season the flank steak generously on all sides with salt and pepper. Place in a shallow baking dish. Sprinkle with garlic and squeeze the two limes over the steak. Pour beer over the top, cover and let marinate for at least 1 hour or up to 4 hours. 

Combine masa harina and salt. Add 1 1/2 cups hot water and mix with a wooden spoon at first to combine, then squeeze water into the flour with your hands. Knead briefly. If dough seems crumbly and dry, add more hot water a little at a time. You don't want it to be sticky, but it shouldn't crack when you roll a piece into a ball. 

Heat a dry comal, cast iron skillet, or nonstick frying pan over medium-high heat.

Form a pool-ball sized piece of dough into a circle, then flatten into a 1/2-inch thick circle. Place dough directly on hot comal and cook, undisturbed until it forms a nice crust, about 2 minutes (turn heat down if it is burning or cooking too fast). Flip and cook other side about 2 minutes more. 

Remove from pan and pinch sides to form a rim. Flatten middle to make an even base. Repeat with remaining dough. 

Heat a grill to medium-high heat. You can also cook the steak in a hot frying pan slicked with oil if you'd like. 

Remove steak from marinade and grill until done to your likeness, about 10 minutes for medium. Let rest 5 minutes then slice into thin, bite-sized pieces. 

Place sopes back over a hot comal (add a slick of oil if you want the bottom to crisp a bit) and let cook until nice and warm. 

Top with slices of steak and any toppings you'd like; avocado slices, watermelon radishes, Queso fresco, sliced red onion. I like to finish them with a drizzle of nice olive oil and a squeeze of lime. Enjoy!