1. Preheat oven to 250º Spread bread on baking sheet and toast until crisp, 30-40 minutes, turning once or twice; set aside to cool.
2. While the bread is toasting and cooling, drop the raisins into a cup of boiling water, soak 5 minutes, then drain on a paper towel.
3. Grind the toasted bread in a blender or food processor, then rub crumbs through a fine sieve into a deep bowl.
4. Add the rest of the ingredients, except the buttermilk, and mix thoroughly.
5. Stirring constantly, add the buttermilk in a fine stream.
6. Taste for seasoning and refrigerate at least 30 minutes.
7. To serve, stir well to recombine and sprinkle nutmeg and cinnamon on each serving.