Sour cherry trees in Brooklyn (and yes, there are a few) are just at their peak, and the greenmarkets are flooding with cherries now as well. Sweet bing cherries are better for eating fresh and plain, but sour cherries (also known as pie cherries) are more flavorful and better for baking. This coffee cake is best hot out of the oven, but stays moist and delicious for days if gently reheated just before serving.......