In a medium saucepan stir together brown sugar and cornstarch; stir in water. Add rhubarb and blueberries. Cook and stir
over medium heat until thickened and bubbly. Add the 1 tablespoon butter and the lemon juice; stir until butter melts. Pour into an
ungreased 1-1/2-quart casserole. (You can use an 8 x 8 inch Pyrex pan.)
While the filling is cooking, make the topping!
Stir together flour, the 1/2 cup granulated sugar, and the baking powder. Add milk and the 1/4 cup butter all at once.
Stir until smooth.
Spoon topping in mounds over hot filling; spread evenly over filling. Sprinkle with a mixture of the 2 tablespoons coarse sugar and
the nutmeg and/or cinnamon. Bake cobbler in a 350 degree F. oven about 35 minutes or until bubbly and a toothpick inserted into
topper comes out clean. Serve warm with ice cream, if desired. Makes 6 servings.