In a medium bowl, mash the beans with a fork or potato masher.
Don't puree them completely; you want some texture and small chunks to remain for the best bite. If the mixture is too dry, add a tablespoon of the reserved bean liquid. 2.
Add the minced onion, parsley, and beaten egg to the mashed beans.
Season generously with salt and pepper and mix until just combined. 3.
Sprinkle in the cornmeal or breadcrumbs, one tablespoon at a time, until the mixture is just stiff enough to be shaped by hand without being overly sticky. Be careful not to add too much, as this can make the croquettes dry. 4.
Shape the mixture into 8-10 small patties or logs, about 2-3 inches across. 5.
Pour about 1/8 inch of oil into a large skillet over medium heat.
Once the oil is shimmering, carefully place the croquettes in the pan, ensuring not to crowd them. You may need to cook in batches. 6.
Fry for about 7-8 minutes total, turning occasionally, until all sides are golden brown and crispy. 7.
Transfer the cooked croquettes to a paper towel-lined plate to drain excess oil.
Serve immediately or keep warm in a 200°F / 95°C oven for up to 30 minutes.
Don't over-mash the beans. Leaving some small chunks provides a better texture and prevents the croquettes from becoming pasty.
