Preheat your oven to 180 degrees. Peel both peaches and plums and remove the pit. Chop them into small chunks and place in a mixing bowl. Sprinkle sugar, cinnamon & honey over the fruits. Mix with a spoon and make sure that the fruits are evenly coated with the sugar. Set aside. Peel peaches by adding them in boiling water for 45 seconds, then adding them in ice-cold water. The skin will peel off easily.
In a medium sized bowl add flour, brown sugar, cinnamon & rolled oats. Mix the ingredients with a fork. Start by drizzling a cup of melted butter and use a fork to combine the ingredients together. The remaining butter should be added a tablespoon as required. Initially the mixture will seem dry but keep mixing and it will start resembling crumbs.
Butter the dish that you are going to serve your crumble in. Any size can be used as long as your fruit can fit into it along with the crumb topping. Just make sure the dish used is either glass, ceramic or another non-reactive material. Some sizes that you can use are an 8 x 8 or 9 x 9 square baking dish, an 8 inch or 9 inch round baking pan or a deep pan pie dish.
Pour fruit mixture into the dish and then sprinkle the crumb topping over the fruit mixture.
Bake in the oven for 35-45 minutes. The crumble is done when the toping is light brown and the fruit juices are bubbling at the edges. You can also bake for 30 minutes and then broil in the end for 5 minutes to give it an even crunchier topping.
The crumble can be served warm or cold. If serving warm, let the crumble cool for at least 15 minutes before serving. This lets the fruit juices thicken and settle down. If serving at room temperature the fruit filling will have thickened up.