Special equipment: two 9-inch-by-5-inch cookie tins with tightly fitted lids, or two 9-inch-by-5-inch loaf pans, wax paper
Preheat the oven to 220 degrees F.
Grease the two cookie tins or loaf pans with butter, then line the bottoms and all four sides of tins with wax paper, making sure to overlap the wax paper by 4 inches on each side.
Whisk together the rye flour, whole-wheat flour, sugar, baking soda and salt in a large bowl. Using a wooden spoon, mix in the buttermilk and corn syrup until fully incorporated. Divide the batter between the two tins and cover tightly with lids or foil, if using loaf pans.
Bake for 12 hours. Remove from oven and let cool for 10 minutes. Remove the lids, upturn the tins, and gently shake each until the bread slides out. Set the loaves on a cooling rack to cool for 30 minutes. Slice and serve with smoked salmon, butter, and cheese such as Fontina or Havarti.
The brown bread may be wrapped in plastic wrap and frozen. It will keep for 3 months.
A viewer or guest of the show, who may not be a professional cook, provided this recipe. It has not been tested for home use.