This is a French Canadian recipe, Gateau des Rois, which Acadians traditionally serve from Epiphany through Shrove Tuesday (Mardi Gras). It is different than the New Orleans style of King Cake.
King Cake—also called Kings' Cake, Gateau des Rois, Cake of Kings, or Twelfth Night Cake—is served from the feast of the Epiphany through Mardi Gras. Traditionally, a trinket is baked inside. In the U.S., the most common trinket is a small plastic baby to represent the baby Jesus. In European countries, the traditional trinket is a bean.
In the recipe below, you may swirl molasses cake batter with white cake batter to make a marble cake, or make the molasses cake alone.
Mix molasses, baking soda, and butter in a large bowl. Add salt, ginger, and boiling water. Stir well and gradually blend in the flour. Stir until smooth. Pour into a buttered and floured 8- or 9-inch square cake pan (if preparing marble cake, use a 9 x 13-inch pan and drop spoonfuls of each batter in alternate layers). Bake at 350 degrees F (180 degrees C) for about 30 minutes (45 minutes for the marble cake), or until cake tests done. Cool and frost with Fudge icing.