Adapted and updated from Sheryl Lehman's Rhubarb Cake in Sharing the Loaves and Fishes compiled by Vashon Presbyterian Church Vashon Island, Washington 1997
Grease and flour an 8x8-inch baking dish. Set aside.
In a large bowl or bowl of a stand mixer, beat together the sugar, oil, buttermilk, egg, vanilla, and spices until well combined. Beat in the remaining ingredients and mix until a thick batter forms. Fold in the rhubarb. Pour into the prepared pan. Set aside.
Mix together the topping ingredients with a fork until it forms coarse crumbs. Sprinkle evenly over the cake.
Bake for 45 minutes or until a toothpick inserted in the middle of the cake comes out clean or with one or two dry crumbs. Cool completely (in pan) on a wire rack.