Preheat the oven to 350°F.
Place the fruit nut bread cubes onto a baking sheet. Melt half the butter and pour over cubes. Bake until lightly golden in color and slightly dried out, about 15-20 minutes.
In a large skillet, melt remaining butter over medium heat, then add the fennel and onions. Cook for 8-10 minutes until softened and a bit caramelized. Transfer the mixture to a large bowl.
Add the toasted fruit and nut bread and stock to the bowl with the onion-fennel mixture and the stock. Mix to combine all ingredients (use your hands if you like -- it’s fun!). The mixture should be moist but not soggy; add a little more stock if you like your stuffing wetter.