Lunar Rhubarb Cake

What You Need

• 1/2 cup butter
• 1 1/2 cups sugar
• 1 egg
• 1 tsp. vanilla
• 2 cups flour
• 1 tsp. baking soda
• 1/2 tsp. salt
• 1 cup buttermilk (1 tbsp vinegar in milk)
• 2 cups chopped rhubarb 1/2" chunks
• 1 tsp. flour
• Topping: cinnamon and brown sugar