Featured in an email this morning from Cooks Illustrated: With a swirl of cinnamon enriching a tender cake and a topping of sweet, nutty streusel, a big slice of coffeecake is pretty hard to beat. Compacting all that goodness into a muffin seemed like a great idea, but most of the coffeecake muffins we tried resembled dry, cottony yellow cupcakes with little or no cinnamon filling. And some recipes simply pack mounds of dry, gritty streusel on top. We set out to make a coffeecake muffin that as good as a regular coffeecake—with the option of taking it to go. Test Kitchen Discoveries For muffins that were rich but not too dense, we cut back on the amount of butter and eggs most coffeecake recipes require, but kept the typical amount of sour cream—it gave the muffins a moist, velvety appeal. For the streusel topping, we cut a little butter and flour into our mixture of nuts, sugar and cinnamon. The added moisture allowed the topping to clump and stay put on top of the muffin. SPECIAL NOTE: Be sure to use muffin-tin liners for this recipe or the cinnamon filling will stick to the pan.