For the Cake:

Preheat the oven to 350 degrees. Grease and flour (or use my “Goop”) in a 9 by 13″glass pan.

In a large mixing bowl, add melted butter, sugar, egg, and buttermilk. Whisk together.

In a smaller bowl, whisk together the flour, baking powder, baking soda, and salt. Add the dry ingredients to the butter/sugar mixture, and beat until just moistened. A few small lumps are fine.

Fold in the chopped rhubarb. Pour and spread the batter into the prepared pan.

In a small bowl, combine the butter and sugar for the topping. Sprinkle evenly over the batter. Bake for 30-45 minutes or until a toothpick comes out clean and the top of the cake is lightly browned.

For the Sauce:

For the sauce, melt butter in a medium saucepan. Add the sugar and evaporated milk or cream. Bring to a boil; cook and stir for 1 minute; it will slightly thicken. Remove from heat and stir in vanilla. The sauce will continue to thicken as it cools, rewarm slightly to serve.

Note on rhubarb: When I bake this in a 9 x 13″ pan, I generally use the smaller amount of rhubarb; it helps the cake hold together better. When baking in a smaller pan, use the larger amount.

note: This streusel forms a gorgeous, slightly crispy layer but softens by the next day. We like it best regardless, but for a more classic streusel, increase butter to 4 tablespoons and add 1/2 cup of flour or use the brown sugar streusel linked in the post.