Ingredients:

  • 1.5 cups (190g) all-purpose flour
  • 0.5 cup (100g) granulated sugar
  • 0.75 cup (180g) Quark or thick Greek yogurt
  • 0.5 cup (115g) unsalted butter, melted and cooled
  • 1 tsp (5g) baking powder
  • 0.5 tsp (3g) salt
  • 1 large egg
  • 2 lbs (900g) Italian prune plums, pitted and sliced into quarters
  • 1 tbsp (8g) cornstarch
  • 1 tbsp (12g) lemon juice
  • 0.75 cup (95g) all-purpose flour
  • 0.25 cup (50g) cold unsalted butter, cubed
  • 3 tbsp (38g) brown sugar
  • 0.5 tsp (3g) cinnamon

Instructions:

  1. Preheat oven to 350°F (175°C) and line a 12x17 inch sheet pan with parchment paper.
  2. Whisk together melted butter and granulated sugar until smooth.
  3. Beat in the egg and Quark until the mixture is velvety and cohesive.
  4. Fold in the flour, baking powder, and salt. Mix until just combined.
  5. Spread the dough evenly across the prepared pan and let it rest for 15 minutes to allow the flour to hydrate.
  6. Toss sliced plums with lemon juice.
  7. Lightly dust the top of the rested dough with cornstarch.
  8. Arrange plum quarters in tight, overlapping rows across the cake, pressing them gently into the dough.
  9. Combine streusel ingredients (flour, cold butter, brown sugar, cinnamon) in a small bowl and mix until crumbly.
  10. Sprinkle the streusel evenly over the plum layer and bake for 45 minutes until the crust is golden brown.