If you can't get hold of dried black or pinto beans, then use tinned in this quick cheat's version!
Save on the hours of soaking and boiling, by using pre-cooked beans and cooking them in a little of their own liquid with onions and garlic until the alliums are cooked out and the sauce thickens.
Serve topped with a dollop of sour cream (or dairy free substitute, or half fat Creme Fraiche, or even Greek yoghurt if you're counting calories) and Fresh Mexican Salsa, as a side dish, or use as a vegetarian filling for tortillas and tacos with the sour cream and salsa and some grated cheese and shredded lettuce or Napa cabbage. These were lovely served alongside my Chicken in Chipotle Chilli Sauce.
If you want to add to the authenticity of the flavour and texture, you can add a further tablespoon of lard to the beans while they're cooking, but I haven't included this in the recipe. For 'Re-Fried' beans, see Notes at the bottom. You could also cook them in an earthenware pot if you have one suitable to go on the hob, which is how they would be traditionally cooked in Mexico.
Serves six, 110 calories per serving.
2 tins of black beans (or pinto beans) with no added sugar or salt , drained and the liquid reserved (480g drained weight, I used Biona organic) 
3 garlic cloves, finely chopped or crushed 
2 small / 1 large onion (120g), finely diced 
1/2 tbsp neutral oil (or lard) 
Salt, to taste
(Optional, extra lard to taste!)
Gently sautee the onions and garlic in the oil in a non-stick pan (you'll need a pan with a tightly fitting lid to cook the beans in, not too large so they don't dry out while you're cooking them) until softened, for around 5 minutes.
Add the beans, and 150ml of the reserved liquid from the tin, along with 1/2 tsp salt (unless your beans were in salted water), give everything a good stir, bring up to a simmer and then turn the heat right down to low and put the lid on the pan.
Simmer for 20 to 30 minutes, stirring occasionally (and making sure your beans don't catch on the bottom of the pan) until the 'sauce' has thickened and the beans are to your desired consistency, then add further salt to taste if necessary and serve hot, topped with sour cream and salsa.
If you want to make 're-fried' beans (or 'well-fried' beans, as 'Frijoles Refritos translates), after cooking the beans as above, fry one finely chopped onion in a generous amount of lard (or neutral oil) in a good heavy-based, large frying pan until soft, and then add half of the beans, mashing them as you cook them. Add the remainder of the beans, spoon by spoon, continuing to mash and stir them as they cook until they're mashed into a rough puree. Once this has dried out a little, and is sizzling around the edges, it's good to go. You can vary this by adding chopped Jalapeno chillies along with the onion.
Both the 'Pot' beans, and the 'Re-fried' beans are good for freezing and re-heat well.