• Preheat the oven to 350℉/176℃. Line the 9x9 baking pan with parchment paper and set aside. Chop the rhubarb into 1/4" pieces and set aside.
  2 1/2 cups rhubarb

For the streusel

• In a medium-sized bowl add softened butter, white sugar, and flour. With a fork or your hands, mix together until a streusel forms. Set in the fridge to chill as you make the cake batter.
  1/2 cup white sugar, 6 tbsp butter, 1 cup all-purpose flour

For the cake

• In a large bowl, add in flour, baking soda, baking powder, cornstarch, and salt. Stir to combine and set aside.
  2 cups all-purpose flour, 3/4 tsp baking powder, 3/4 tsp baking soda, 1 tbsp cornstarch, 1/4 tsp salt
• In another large bowl, add in white sugar and eggs. Whisk together to combine for 2-3 minutes until air bubbles appear.
  2 large eggs, 3/4 cups white sugar
• Add in the butter and oil and continue whisking for another 2-3 minutes.
  1/2 cup butter, 1/4 cup oil
• Add in the sour cream and vanilla and whisk until combined.
  3/4 cups full-fat sour cream, 1 tbsp vanilla
• Mix in the dry ingredients with the wet using a spatula until a soft cake batter forms. Don't over-mix!
• Spread evenly into the pan. Then sprinkle the rhubarb evenly on top, and finish with the streusel.
• Bake for the cake 40-50 minutes or until a toothpick inserted comes out clean. Allow the cake to cool, slice, and enjoy!
• This rhubarb cake is delicious and so easy to bake. It's best served fresh or next day.