Ingredients:

  • 1/2 cup (100g) unsalted butter, cold and cubed
  • 1 cup (200g) packed light brown sugar
  • 1 1/2 cups (190g) all-purpose flour
  • 2 tsp (10g) ground cinnamon
  • 1/4 tsp (1.5g) salt
  • 2 cups (300g) fresh rhubarb, chopped into 1/4-inch pieces
  • 1/4 cup (50g) granulated sugar
  • 1 tbsp (8g) cornstarch
  • 2 cups (250g) all-purpose flour
  • 1 tsp (5g) baking powder
  • 1/2 tsp (3g) baking soda
  • 1/2 tsp (3g) salt
  • 3/4 cup (170g) unsalted butter, softened
  • 1 cup (200g) granulated sugar
  • 2 large eggs, room temperature
  • 1 tsp (5ml) vanilla extract
  • 1 cup (240g) full-fat sour cream

Instructions:

  1. In a medium bowl, combine flour, brown sugar, cinnamon, and salt. Work the cold butter into the mixture using your fingers or a pastry cutter until it forms pea-sized clumps. Set aside in the fridge.
  2. Toss the chopped rhubarb with granulated sugar and cornstarch until evenly coated.
  3. Grease a 9-inch square pan and line it with parchment paper.
  4. Beat the softened butter and sugar on medium-high until light and fluffy (about 3 minutes). Mix in the eggs one at a time, followed by the vanilla extract.
  5. Whisk together the flour, baking powder, baking soda, and salt. Gradually add the dry ingredients to the butter mixture, alternating with the sour cream. Mix until just combined.
  6. Spread half of the batter into the pan. Scatter the rhubarb filling evenly over the top. Spread the remaining batter over the rhubarb and top with the chilled streusel, pressing lightly.
  7. Bake at 350°F (175°C) for 35-40 minutes until the edges pull away from the pan and a toothpick inserted into the center comes out clean.
  8. Let the cake cool in the pan for at least 20 minutes before slicing.