Fresh Spring Asparagus Soup

Name: Fresh Spring Asparagus Soup
Ingredients: 1 Tablespoon Butter Or Oil; 1 whole Small Leek, Sliced In Half Moons (white Part Only); ½ whole Large Onion, Diced; 6-¼ ounces, weight Yukon Gold Potatoes, Very Small Dice; 1-¾ pounds, 2-⅞ ounces, weight Fresh Asparagus, Cut Into Small Chunks; 2 teaspoons Fresh Thyme; 2 teaspoons Fresh Rosemary; 4 cups, 3 tablespoons, 1-⅞ teaspoons, ¼ pinches Low Sodium Chicken Or Vegetable Stock; ½ cups Plain Yogurt, Whole Or Half Fat; Fresh Ground Salt And Pepper To Taste