Pierce potatoes with a fork in several places. Arrange on a paper towel in the microwave. Microwave at full power until tender, 12-14 minutes. Transfer to a board and cut in half, lengthwise. Let stand until cool enough to handle, about 10 minutes.
Meanwhile, preheat the oven to 325°F. In a large bowl, beat together the goat cheese, 1/2 cup brown sugar and eggs until smooth, 1 minute. Scoop potato flesh into the bowl; beat until smooth, 1 minute. Add the half & half, cinnamon, allspice and salt. Beat together until combined.
Place butter in 9" square (2qt.) baking dish. Microwave at full power until melted, 1 minute. Brush butter to caot bottom and sides of dish. Pour excess butter in a small dish and stir in remaining 1 tbsp. brown sugar. Scrape potato mixture into the baking dish and spread level. Sprinkle pecans on top and drizzle with butter/sugar mixture.
Bake until heated through, 45 minutes. Serve hot.Tip: For a crowd, this recipe is easily doubled and prepared in a 13"x9" dish.Make a head: you can cook the sweet potatoes up to 2 days in advance; store them in the refrigerator, and bring them to room temperature before continuing. You can also prepare the entire casserole through step 3 early in the day and refrigerate it. Bake, covered, for 15 minutes, then uncover and bake until heated throgh, 40-45 minutes.