Preheat the oven to 350 degrees F. Grease and flour a 9x13 inch baking dish.
In a large bowl, stir together the sugar, brown sugar, baking soda, baking powder, salt and flour. Stir in the eggs and sour cream until smooth, then fold in the rhubarb. Pour into the prepared dish and spread evenly.
In a small bowl, stir together the sugar, brown sugar and butter until smooth. Stir in the flour and mix until crumbly. Sprinkle the mixture evenly on top of the cake then dust lightly with cinnamon.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 45 minutes. The butter and sugar will brown and caramelize for a crispy top layer.
Though this coffee cake is delicious anytime, it’s especially delicious with, well, coffee.