Preheat the oven to 350 degrees F. Grease and line with parchment paper a 13 by 9 by 2 rectangular cake pan. In a saucepan, over medium heat, add the buttermilk and butter. When the butter has melted, remove from the heat and cool. Whisk in the eggs and sugar. Whisk until smooth. Sift the flour, baking soda and spices together. Stir the flour. Mix well. Pour into the prepared pan. Bake for 30 to 35 minutes or until the center of the cake is done. Remove the cake from the pan and cool on a wire rack. Slice the cake into 12 servings. To serve, spoon the sauce in the center of each plate. Place a piece of cake in the center of the sauce. Garnish with whipped cream and mint.