your fingers the matzo meal, the remaining 1/2 cup sugar, margarine, and nutmeg until fine crumbs form. Squeeze to compact into lumps, then crumble over rhubarb mixture. Bake in a 375'F. oven until cobbler is bubbling in center and top is golden brown, about 1 hour. Let cool 15 minutes; spoon cobbler into bowls and top with sorbet, if desired.