Yes, you can bake this cake as a tray bake. You will need a 13" x 9" baking tray that is deep enough to hold all the batter. Line the tray with baking parchment to prevent sticking, and bake for 20 to 25 minutes, or until a wooden skewer inserted into the cake comes out cleanly. You can also use this mixture to make individual coffee walnut cakes in a muffin tin. Grease the muffin tins with a little butter, or brush lightly with sunflower oil before spooning the mixture into the holes. You may find the muffins will need slightly less cooking time. Check for doneness after about 18 minutes. If you bake your coffee cake in either of these ways you will find you have too much frosting because there are no layers, so you can just halve the quantities for the coffee buttercream.