In a medium mixing bowl, stir the baking soda into the boiling water until completely dissolved. Add the fancy molasses and sour milk (or milk and vinegar mixture), and stir to combine. Let the mixture cool slightly so it doesn’t affect the flour when mixed.

In a large mixing bowl, whisk together the whole wheat flour, all-purpose flour, and salt. Gradually pour the wet ingredients into the dry, stirring just until a thick, sticky batter forms. This is not a dough you knead — the texture should be more like a quick bread batter.

Preheat your oven to 350°F (175°C). Grease a standard loaf pan well. Pour in the batter and smooth the top with a spatula.

Bake for 45 to 50 minutes, or until a toothpick inserted into the center comes out clean and the top feels firm. Let the bread cool slightly in the pan before turning it out onto a wire rack to cool completely.