Here's a coffee cake in the tradition of Moravian sugar cake, the yeast-raised cake made from potato dough and covered with a buttery sugar topping. Our version uses pumpkin instead of potato and has an orange hue that's quite pretty. It makes a big, impressive, and rather unique cake if you need to feed a whole gang.–The Old Farmer's Almanac Everyday Baking Cookbook
Pour the water into a small bowl and sprinkle with yeast. Stir to blend, then set aside for 5 minutes.
Meanwhile, combine the pumpkin, milk, sugar, oil, egg and yolk, salt, and vanilla in a large bowl. Stir in the dissolved yeast. Whisk well. Add 2 cups of the flour and beat well with a wooden spoon for 2 minutes. Stir in the remaining 1 cup of flour, ⅓ cup at a time, beating well with the spoon for 1 minute after each addition. Do not skimp on the time: This hand beating eliminates the need to knead. Set the dough aside long enough to butter a 13x9-inch baking pan. Scrape the dough out of the bowl and into the middle of the baking pan. Set aside for 5 minutes.
Tear off a sheet of plastic wrap a little larger than your pan and oil it or coat it with nonstick spray; the oil will ensure that the plastic doesn't stick to the dough. Place the plastic on top of the dough with the oiled side toward the dough, center the plastic, and press the dough out evenly in the pan. Take your time to make it reasonably level. Remove the plastic and cover the pan with a fresh sheet of plastic wrap. Set aside at room temperature for 1-½ hours to rest (it won't seem to rise very much).
While the dough rests, put the brown sugar, walnuts, and cinnamon into a food processor and pulse until the nuts are very finely chopped. Set aside.
After 1-½ hours have passed, preheat the oven to 350° F. Remove the plastic and cover the dough evenly with the brown sugar topping. Using a fingertip, make 12 deep indentations in the dough (three evenly spaced rows of four holes). Melt the 7 tablespoons of butter and spoon evenly over the top, letting some of it drip into the holes. Bake on the center oven rack for 35 minutes. The top will be a rich golden brown, but the best indicator of doneness is total baking time. Cool in the pan on a rack for 10 minutes before slicing and serving.