How to Make It
In a bowl, whisk the egg. Whisk in both cheeses, the oil, salt and pepper. Stir in the matzoh meal. Let stand at room temperature for 10 minutes, then gently form into 1-teaspoon-size balls.
In a medium saucepan, bring the stock to a boil with the garlic. Add the matzoh balls, cover and simmer over moderate heat for 30 minutes. Add the carrot, cover and simmer until the carrot is tender and the matzoh balls are puffed and light, about 10 minutes longer. Ladle into bowls. Garnish with tarragon and grated cheese.