Preheat the oven to 350 degrees F. Spread the walnuts on a baking sheet and toast in the oven for 5 minutes, then let cool slightly. (Leave the oven on.) When cool enough to handle, roughly chop the nuts; set aside. Dust a baking stone or baking sheet with cornmeal and set aside.
In a large bowl, mix together the flours, baking powder, baking soda, salt, sugar and caraway seeds using a fork. With a pastry blender or 2 knives, cut in the butter until the mixture resembles coarse sand. Add the raspberries and chopped walnuts; toss gently.
In a small bowl, whisk together the buttermilk and egg; add to the flour mixture and stir gently with a wooden spoon just until mixed. (Do not overmix.)
For a higher, sturdier-structured bread, turn the dough onto a floured surface and knead lightly about 5 times, adding additional flour if the dough is too sticky. (This step is optional.)
Mound the dough onto the cornmeal-dusted baking stone and bake until the loaf is slightly golden and sounds hollow when tapped, 55 to 60 minutes. Cool completely before slicing.
If you don't have buttermilk, use any of these substitutions: 1 tablespoon vinegar plus enough milk to make 1 1/3 cups liquid; or 1 cup plain yogurt plus 1/3 cup milk or water; or 1 1/3 cups kefir.