To make the sponge: Mix the sponge ingredients together, and let rest at room temperature, covered, for 3 to 4 hours, or overnight.
To make the dough: Stir down the sponge, and add the salt and flour. Mix and knead the dough until it's smooth and elastic. Knead in the mixed seeds. Place the dough in a greased bowl, turning to coat its surface with oil. Cover and let rise in a warm spot for 1 1/2 to 2 hours, until doubled in size.
Turn the dough out onto a lightly greased surface, and form it into a ball. Place on a lightly greased or parchment-lined baking sheet, or into an ovenproof crock (like a dutch oven). Cover and let rise for about 1 hour. Towards the end of the rising time, preheat the oven to 450°F.
Uncover the loaf, and gently but firmly slash it across the top, then spritz it with water. Bake the bread for 30 to 35 minutes, until it's deep golden brown. Remove it from the oven and place it on a rack to cool. Cool completely before slicing.