Fresh, candied and ground ginger each lend their own flavor dimensions to this dark and spicy, warm and moist gingerbread.
To make gingerbread: Preheat oven to 350 degrees F. Coat an 8-inch square baking pan with cooking spray.
Whisk together flour, brown sugar, baking soda, ground ginger, cinnamon, mace, cloves and salt in a mixing bowl. Use your fingers to break up any sugar clumps if necessary.
Beat together molasses, orange juice, egg, egg whites, oil, crystallized ginger, fresh ginger and vanilla in another mixing bowl with an electric mixer on medium speed until smooth. Add the dry ingredients and mix on low speed just until blended. Transfer the batter to the prepared pan. Bake until a toothpick inserted into the center of the cake comes out clean, about 30 minutes. Let cool in the pan on a rack for about 15 minutes.
To make sauce: While the gingerbread is baking, whisk together granulated sugar and cornstarch in a saucepan. Whisk in orange and lemon zests and orange and lemon juices. Cook over medium heat, whisking constantly, until the sauce thickens and boils. Cook, stirring, for 1 minute. Strain the sauce through a fine sieve into a bowl and whisk in rum and butter.
To serve, remove the cake from the pan, cut into 9 squares and serve warm with warm citrus sauce.
Make Ahead Tip: The sauce (Step 4) can be made several days ahead and gently reheated at serving time.
1 starch, 2 other carbohydrate, 1 fat