1 cup dried black beans, washed and picked over
1 cup dried white beans, washed and picked over
8 cups water
4 slices bacon, coarsely chopped
2 lg. onions, diced
2 carrots, peeled and diced
2 garlic cloves, minced
1 tsp. coarse salt
1 lg. tomato, diced
2 bay leaves
2 canned chipotle chiles
6 cups vegetable stock
1 lime, halved
Place the black beans in a medium saucepan with 4 cups of the water and bring to a boil. Place the white beans in another medium saucepan with remaining 4 cups of water and bring to a boil. Reduce heat to low, cover and cook until both pots of beans are soft, about 1 hour. Remove from the heat.
In another large saucepan, saute 2 slices of the bacon over medium heat until crispy. Remove bacon, saving grease in pan. Add 1/2 of the diced onions and all of the carrots and cook over medium low heat until onions are lightly browned, about 15 minutes. Then add 1/2 of the garlic and 1/2 teaspoon of the salt, stirring constantly, until the garlic aroma is released, 12 minutes. Stir in the black beans and their liquid, along with the tomato, 1 bay leaf and 1 chipotle chile. Pour in 3 cups of the vegetable stock. Turn up the heat and bring to a boil. Reduce to a simmer and cook, uncovered, stirring occasionally, an additional 30 minutes.
Repeat the entire procedure with the white beans, using the remaining bacon, onion, garlic, salt, bay leaf, chipotle chile and stock.
Remove bay leaves and transfer black bean mixture to a blender in batches and puree until smooth, pulsing the machine on and off until it begins to liquefy. (Be sure to leave space for the air to escape). Return to a clean saucepan. Rinse out blender and repeat with white bean mixture.
Reheat soups over low heat, squeeze half of a lime into saucepans and stir to blend. Adjust seasoning.
Using two ladles, carefully ladle the two soups side by side into one bowl, so that half is black and half is white. Garnish with Tomatillo Salsa.