2 1/2 cups unbleached all-purpose flour (12 1/2 ounces)
2/3 cup granulated sugar (about 4 3/4 ounces)
1/2 teaspoon table salt
16 tablespoons unsalted butter (2 sticks) plus 2 tablespoons, cut into 1/2-inch pieces and softened to cool room temperature
1/4 cup packed brown sugar (1 3/4 ounces), light or dark
1/2 cup rolled oats (1 1/2 ounces), old-fashioned
1/2 cup pecans (2 ounces), chopped fine
3/4 cup rasberry preserves (8 1/2 ounces)
1 cup fresh raspberries (5 ounces)
1 tablespoon lemon juice from 1 lemon
Adjust oven rack to middle position; heat oven to 375 degrees. Line 9×13 pan with nonstick tin foil. If ou do not have nonstick tin foil, go buy some then report back. Seriously, I think the raspberry would stick something fierce. Line or not as you wish, but don’t come crying to me.
In food processor, process flour, granulated sugar, and salt until combined, about 5 seconds. Scatter 16 tablespoons butter pieces over flour mixture and pulse until mixture resembles damp sand, about twenty 1-second pulses.
Measure 1 1/4 cups (6.5 oz) flour mixture into medium bowl and set aside; distribute remaining flour mixture evenly in bottom of prepared baking pan. Using hands or flat-bottomed measuring cup, firmly press mixture into even layer to form bottom crust. Bake until edges begin to brown, 14 to 18 minutes.
While crust is baking, add brown sugar, oats, and nuts to reserved flour mixture; toss to combine. Work in remaining 2 tablespoons butter by rubbing mixture between fingers until butter is fully incorporated. Pinch mixture with fingers to create hazelnut-sized clumps; set streusel aside.
Combine preserves, raspberries, and lemon juice in small bowl; mash with fork until combined but some berry pieces remain.
Spread filling evenly over hot crust; sprinkle streusel topping evenly over filling (do not press streusel into filling). Return pan to oven and bake until topping is deep golden brown and filling is bubbling, 22 to 25 minutes. Cool to room temperature on wire rack, 1 to 2 hours; remove from baking pan by lifting foil extensions. Using chef’s knife, cut into squares and serve.
Strawberry Rhubarb variation:
Make strawberry rhubarb jam by combining 1 cup each sliced strawberries and diced rhubarb in a saucepan with 1/3 c sugar. Cook until soft and well combined. Use this in place of the jam and a cup of sliced strawberries in place of the raspberries.