We first had this soup in San Miguel de Allende, and this adaptation is the result of several attempts -- I think we got it right! Believe it or not, the trick seems to be the ketchup and Parmesan--don't know why, but it works.
SOPA DE AJO (Garlic Soup)
10 large cloves of garlic, peeled (for starters - we often use more)
2 Tablespoons olive oil
2 cans beef broth with 2 cans water (or if you have 5 cups homemade beef stock, it's better)
1-2 dried Bay leaves
1 bunch fresh cilantro, chopped (reserve some for garnish)
1/4 c. ketchup
1/3 Cup grated Parmesan cheese ( the cardboard Kraft kind works)
2 beaten egg yolks
4-5 slices buttered bread
Mince or mash garlic and sauté in olive oil until tender. Stir in broth, water (if using canned broth), cilantro, and bay leaf. Cover and simmer for about an hour--add catsup and simmer for about 15 minutes uncovered.
Meanwhile, butter bread and toast it in a 325 degree oven for 10-15 min -- croutons. Quarter slices and use 2-3 quarters per bowl. Strain soup. I use a mesh colander. Add 1 Cup soup gradually to beaten egg yolks and return to saucepan to thicken slightly, stirring constantly. Add Parmesan cheese until it's incorporated and doesn't look grainy--5 min? Put toast quarters in bowl and pour hot soup over--garnish with more cilantro--serves about four people, and it's very good.