In a cast-iron skillet, toast the ginger, cardamom, coriander, fenugreek, nutmeg, cloves, cinnamon, and allspice over low heat. Do not burn; this should only take a minute or so. Set aside to cool.
Combine the spices, onions, garlic, 1 tablespoon of the salt, and 3 tablespoons water in a small jar of a blender and blend until smooth.
Combine the paprika, cayenne pepper, black pepper, and the remaining tablespoon of salt in the skillet and toast over low heat for a minute or so. Stir in the water, ¼ cup at a time. Then stir in the blended mixture. Stirring vigorously, cook over the lowest possible heat for 10-15 minutes.
Transfer the berbere to a jar, packing it in tightly. Let the paste cook to room temperature, then cover with a film of oil. Store in the refrigerator between use.