In a large saucepan combine the 1 cup sugar and cornstarch. Stir in liqueur or orange juice. Add rhubarb. Cook and stir until thickened and bubbly. Remove from heat. Keep hot.
In a medium bowl stir together 1 cup flour, 2 tablespoons sugar, and baking powder. Cut in the butter until mixture resembles coarse crumbs. Stir together egg and milk; add to flour mixture, stirring just to moisten. Turn out onto lightly floured surface. Knead 5 or 6 times. Roll dough to an 11x4-inch rectangle. Cut lengthwise into 1/2-inch-wide strips.
Stir strawberries into rhubarb mixture. Turn hot fruit mixture into a 2-quart rectangular or oval baking dish. Weave dough strips atop fruit mixture to make a lattice top, trimming strips to fit dish. Place baking dish on a foil-lined baking sheet. Bake in a 400 degree F oven for 20 to 25 minutes or until fruit is tender and lattice top is golden. Serve warm with cream or ice cream, if desired. Makes 6 to 8 servings.