Vegetable Soup with Greek Yogurt

Name: Vegetable Soup with Greek Yogurt
Ingredients: 3 onions, chopped; 6 carrots and/or other root veg, peeled and chopped; 4 cloves of garlic, peeled and chopped. Use more or less depending upon how you feel about garlic.; 1 bunch Swiss chard and/or other dark, leafy greens, chopped; 1 knob of butter (maybe 3 tbs); 1 glug of olive oil (maybe 3 tbs); 2 liters vegetable stock (I use bouillion cubes); enough liquid to cover the veg; 1 bay leaf; Ground pepper, to taste; Salt, to taste (since I use bouillon cubes, I never have to add salt); 14 ounces Greek-style full-fat yogurt