Slightly adapted from King Arthur Flour
3 cups whole wheat flour
Preheat the oven to 180C (350F). Grease and flour 22cm x 33 cm (9x13-inch) pan.
Mix the flour, sugar, and ginger in a large bowl. Cut in the butter until the mixture is crumbly, like coarse cornmeal. Set aside 1 cup of the mixture. Add the molasses, eggs, water, and baking soda to the remaining crumb mixture and hand-whisk until smooth. Pour the batter into the prepared pan and sprinkle the reserved crumb mixture evenly over the top of the batter.
Bake for 35-45 minutes, or until a cake tester comes out clean. Cool to lukewarm before serving.