Marionberry Oat Crumble Bars

Marionberries — a blackberry hybrid developed at Oregon State University and grown almost exclusively in the Willamette Valley — make these press-in bar cookies a quintessentially Pacific Northwest treat, perfect for summer farmers markets and potlucks.

Serves: 16

Ingredients

Crust and Crumble

• 200g (1 3/4 cups) all-purpose flour
• 150g (1 1/2 cups) old-fashioned rolled oats
• 150g (3/4 cup) packed brown sugar
• 1/2 tsp baking powder
• 1/4 tsp fine salt
• 170g (3/4 cup / 1.5 sticks) cold unsalted butter, cut into cubes
• 1 tsp vanilla extract

Marionberry Filling

• 600g (about 4 cups) fresh or frozen marionberries (or blackberries)
• 100g (1/2 cup) granulated sugar
• 2 tbsp (16g) cornstarch
• 1 tbsp fresh lemon juice
• Zest of 1/2 lemon

Instructions

1. Preheat oven to 175°C (350°F). Grease a 23x33cm (9x13-inch) baking pan and line with parchment, leaving an overhang on two sides.
2. Combine flour, oats, brown sugar, baking powder, and salt in a large bowl. Add butter and vanilla; use your fingers or a pastry cutter to work the butter in until the mixture clumps together in pea-sized pieces.
3. Press roughly two-thirds of the oat mixture evenly into the bottom of the prepared pan, pressing firmly to form a compact crust. Refrigerate 10 minutes while you make the filling.
4. Toss marionberries with sugar, cornstarch, lemon juice, and zest in a medium bowl. Spread berry mixture evenly over the chilled crust.
5. Scatter the remaining oat crumble over the berry layer, pressing lightly.
6. Bake 40–45 minutes, until the crumble is golden and the berry filling is bubbling at the edges. Cool completely in the pan on a wire rack, at least 1 hour, before lifting out and slicing into bars.

Cook's Notes: Frozen marionberries work beautifully here — no need to thaw them before tossing with the filling ingredients, but add 5 extra minutes to the bake time. The bars slice cleanest after a full cool-down. Store covered at room temperature up to 3 days, or refrigerate up to 5 days.