8 tablespoons unsalted butter (1 stick), at room temperature
1 cup packed dark brown sugar
1/2 cup dark molasses, such as Grandma's Robust
2 large eggs, at room temperature
Heat oven to 350F and arrange a rack in middle. Coat a 9-inch-by-5-inch loaf pan with butter, dust with flour, and tap out excess.
Combine flour, ginger, baking soda, cinnamon, salt, allspice, and cloves in a large bowl. Whisk to aerate and break up any lumps; set aside. In a separate medium bowl, stir together buttermilk and vanilla until combined.
Combine butter and brown sugar in the bowl of a stand mixer fitted with a paddle attachment. Beat on medium speed until light in color and fluffy, about 5 minutes. Beat in molasses until well combined then add eggs, one at a time, beating after each addition until well incorporated.
Stop mixer and scrape bowl and paddle (mixture will look separated and curdled). Add one third flour mixture beating on low speed just until flour is incorporated. Add half buttermilk mixture and once batter is smooth add another third flour mixture. Add remaining buttermilk and mix until incorporated. Add remaining flour mixture, and beat until incorporated and smooth.
Pour into prepared pan. Bake until a toothpick inserted in the middle comes out clean and cake is pulling away from sides of pan, about 45 minutes. Cool cake in pan for 10 minutes and then turn out onto a rack to cool completely.