Oat crunch topping:
¾ cup all-purpose flour (94g)
¼ cup brown sugar (50g)
2 tbsp. granulated sugar (30g)
Pinch of salt
5 tbsp. melted butter (72g)
½ cup old fashioned rolled oats (45g)
Blackberry filling:
16oz. fresh or frozen blackberries (500g)
¼ cup sugar (50g)
Cake:
3 cups all-purpose flour (375g)
1 tbsp. baking powder (12g)
½ tsp. baking soda (3g)
½ tsp. salt (2g)
1 cup butter (230g)
1 cup sugar (200g)
1 tbsp. vanilla (15ml)
3 eggs
1 cup sour cream (240ml)
Glaze:
¼ cup powdered sugar (31g)
2–3 tsp. water (10-15ml)
Preheat oven to 350°F (176°C.) Grease and flour a 9″x13″ (23cm x 33cm) baking pan.
To make the oat crunch topping: Add the flour, brown sugar, granulated sugar and salt to the bowl of a food processor. Pulse to combine well. Add the melted butter and pulse until large crumbs form, about 1 minute. Remove bowl from food processor and stir in the oats with a spoon. Set aside.
To make the blackberry filling: In a medium sized bowl combine the blackberries with the sugar, stirring well. Set aside.
To make the cake: In a large bowl, combine the flour, baking powder, baking soda and salt. Set aside.
In a separate large bowl, use an electric hand mixer to cream together the butter and sugar. Add the vanilla and eggs and mix to combine well, about 30 seconds.
Alternately add portions of the sour cream and the dry mixture to the creamed butter mixture, beating briefly until well combined.
Pour the cake batter into the prepared pan. Top the cake batter with the blackberry filling. Sprinkle over the oat crunch topping.
Bake for 1 hour until a toothpick comes out clean. Cool completely then drizzle with glaze. Serve warm or cooled.