First things first, let's get those ingredients together.
Preheat your oven to 350 degrees F (175 degrees C). Make sure to grease and flour a 9x13-inch baking dish.
Now, onto the cake mix: In a big bowl, mix together flour, sugar, baking soda, and salt.
Once that's all blended, add in the eggs and sour cream, and give it a good stir until it's nice and smooth. Then, gently fold in the rhubarb.
Pour this delicious mix into your prepared baking dish, making sure it's spread out evenly.
Next up, let's make that yummy streusel topping: In another bowl, mix together the sugar and butter until it's nice and smooth. Then, stir in the flour until it's all crumbly.
Sprinkle this delightful mixture over the top of your cake batter, and then give it a light dusting of cinnamon.
Pop it in the oven and let it bake for about 45 minutes, or until a toothpick inserted into the center comes out clean.
Once it's done, take it out, let it cool for a bit, then serve it up and enjoy the deliciousness!