Clean the rhubarb and chop it into slices, about 1,5 cm/ 0.6 inches thick. Next, peel the apples, remove the core and chop the apples into chunks.
Preheat the oven to 200 degrees Celsius/ 400 degrees Fahrenheit.
Cook: Melt the butter in a pan and saute the rhubarb and the apples for a couple of minutes. Add the cinnamon and the honey and continue cooking until all the liquid has evaporated; it won't take long. The apple chunks will remain more or less whole, while the rhubarb will almost disintegrate and form a kind of sauce for the apples. Taste and adjust the taste with a little bit more honey, if necessary. Don't make it too sweet; remember that the crumble is sweet, and you will serve this with more sweet stuff. Pour the mixture in a medium casserole form.
Toast the almond slivers in a small pan without adding any fat. Keep an eye on them and shake the pan regularly. Transfer to a plate as soon as they start to get golden and fragrant.
Crumbles: Place the flour and the chopped butter in a bowl. Rub with your fingers until you obtain crumbs. Add the sugar and about 2/3 of the almonds and mix them. Distribute the crumble evenly over the rhubarb-apple mixture in the casserole form. Sprinkle with the remaining almond slivers.
Bake for about 20 minutes or until the crumbles are golden brown.
Serve hot, warm, or cold with custard or vanilla sauce or vanilla ice cream. The vanilla ice cream is perfect when the crumble is still hot or warm.