1. Preheat the oven to 375 degrees F. Grease a 2 quart casserole dish with 2 teaspoons butter. In a saucepan, combine the rhubarb, 2 cups sugar, 4 tablespoons of butter and lemon juice. Stir and cook until a syrup begins to form and the rhubarb starts to soften, about 6 to 7 minutes. Remove from the heat. Using an electric mixer, cream the remaining 2 teaspoons butter and sugar together. Add the egg. Slowly add the baking powder, flour, nutmeg, cinnamon, vanilla, and buttermilk. Mix until thoroughly incorporated and the batter resembles a cake batter. Pour the rhubarb into a greased 2 quart casserole dish. Pour the batter over the rhubarb. Bake for 30 to 35 minutes or until the center is done. Spoon a heaping serving of the cobbler onto a shallow bowl. Place one scoop of the ice cream to the side. Garnish with fresh mint, powdered sugar, and cinnamon sugar.