Filling
Roux
Batter
Topping
Prep: Let eggs and sourcream come to room temp. Preheat oven to 163°C, middle rack position. Line a 23x23 cm baking pan with parchment or foil.
Filling: Whisk all filling ingredients in a small bowl until fully combined. Set aside.
Roux: In a microwave-safe bowl, combine oil and flour. Microwave in 30-second intervals, stirring each time, until mixture bubbles vigorously, about 60-90 seconds total (approx. 120°C). Allow to cool.
Creaming: In a large bowl, cream sugar and butter with a hand mixer on medium speed until pale and fluffy (about 3 mins). Add eggs one at a time, mixing thoroughly after each. Add vanilla and mix until smooth.
Dry Ingredients: Sift baking powder, baking soda, and salt into the bowl with the butter mixture . Mix well to evenly distribute, scraping bowl halfway through.
Flour & Wet Ingredients: Alternate adding flour with sour cream and cooled roux mixture, starting and ending with flour, mixing just until combined.
Assemble: Spread half the batter evenly in the prepared pan. Sprinkle filling evenly on top. Gently spread the remaining batter over the filling.
Topping: whisk flour, cornstarch, cinnamon, cardamom, salt, and sugar. Rub butter into dry ingredients with your fingers until mixture resembles coarse crumbs. Sprinkle topping evenly over the cake.
Bake: Bake in preheated oven for 60-75 minutes, until golden brown and a skewer inserted in the centre comes out clean.
Cool & Serve: Cool cake in the pan for 15 minutes, then lift it out onto a wire rack.
