Step 1Heat the oven to 350 degrees.
Step 2Combine the fruit, butter and lemon zest in a saucepan. In a small bowl, combine 3/4 cup of the sugar and the cornstarch and stir well. Add the cornstarch mixture to the fruit mixture. Cook over medium heat, stirring constantly, until the sugar has dissolved and the mixture has thickened slightly, about 5 minutes.
Step 3Pour the fruit mixture into a 9x7-inch baking dish and let it stand while making the topping.
Step 4Sift the flour, the remaining 3/4 cup of sugar, baking powder and salt into a mixing bowl. Add the milk, shortening, vanilla and egg. Beat at medium speed for 2 or 3 minutes. Spoon the batter over the fruit mixture.
Step 5Bake the cobber until it's golden brown and the edges are bubbly, 45 to 50 minutes.