Cook the beans: Rinse the dried beans and place them in a large pot with 10 cups water, 0.5 onion (halved), and 2 garlic cloves (smashed). Bring to a boil over high heat, skim foam, then reduce to a gentle simmer, partially cover, and cook 1 hour 30 minutes to 2 hours until the beans are tender and creamy when pressed. Stir in 2 tsp kosher salt during the last 20 minutes. Reserve 1.5 cups bean cooking liquid, then drain the beans and discard the onion and garlic.
Make the tortilla dough while the beans simmer: In a mixing bowl, whisk together the flour, baking powder, and 1 tsp kosher salt. Work in the vegetable shortening with your fingers until the mixture looks sandy. Add the warm water gradually, mixing until a soft, slightly tacky dough forms; knead 3–5 minutes until smooth. Cover and rest 30 minutes.
Portion the tortillas: Divide the dough into 8 equal balls, cover, and let sit while you prepare the fillings.
Make the crema: In a small bowl, whisk the sour cream, heavy cream, and fine salt until smooth and pourable. Refrigerate until needed.
Refry the beans: Heat the neutral oil in a large skillet over medium heat. Add 0.5 onion (finely chopped) and cook, stirring, until translucent, 3–4 minutes. Add 2 garlic cloves (minced) and cook until fragrant, 30 seconds. Add the cooked beans and 0.75–1 cup reserved bean liquid; mash with a potato masher, then simmer 5–8 minutes, stirring, until thick, smooth, and spreadable. Adjust the consistency with more liquid if needed and season to taste. Reduce heat to low to keep warm.
Cook the tortillas: Heat a comal or cast-iron skillet over medium-high until hot. On a lightly floured surface, roll one dough ball into an 8–9 inch round about 1/8 inch thick. Cook 45–60 seconds, flip and cook another 45–60 seconds until the tortilla puffs with scattered brown spots; flip once more if needed. Stack cooked tortillas in a towel to keep warm and repeat with remaining dough.
Assemble the baleadas: Lay a warm tortilla flat. Spread 1/4–1/3 cup hot refried beans over one half, drizzle 1–2 tbsp crema, and sprinkle 2–3 tbsp queso fresco. Add avocado, hot sauce, and pickled red onions (for serving), if desired. Fold the tortilla in half to enclose the filling. Repeat with remaining tortillas and serve immediately.