Prick the sweet potatoes all over with a fork, then put them in a roasting pan and roast for 30 minutes. Toss the bananas into the pan and continue roasting until both the bananas and potatoes are very soft, 10 to 15 minutes. Set aside to cool but leave the oven on.
When the potatoes are cool enough to handle, scoop out the flesh into a large mixing bowl. Peel the bananas and add their flesh to the bowl along with the honey and 1 stick of the butter. Season with salt and beat vigorously with a wooden spoon until everything is well combined and the mixture is fluffy. Spoon into an ovenproof serving bowl and smooth the top.
In a separate mixing bowl, use your fingers to rub together the pecans, brown sugar, flour and the remaining stick of butter until the mixture has the consistency of coarse crumbs. Sprinkle the crumb mixture over the sweet potatoes and return to the oven. Cook until the crumbs are golden, about 20 minutes. Serve hot.