With their gooey fillings and high sugar content, raspberry streusel bars—and bar cookies in general—can be nearly impossible to remove from their baking pans, no matter how well the pan is greased. Don’t get us wrong—we certainly don’t mind eating the broken bits straight out of the pan. But we also like the look of trim, neat edges.
After baking countless batches, we finally found a method that works every time: Lining the pan with an aluminum foil or parchment “sling” before baking. Once cooled, the bars may be lifted easily from the pan—casualty-free.
MAKING A FOIL SLING
STEP #1 Fold two long sheets of aluminum foil so that they are as wide as the baking pan (if the dish is rectangular, the two sheets will be different sizes). Lay the sheets of foil in the pan, perpendicular to one another, with the extra foil hanging over the edges of the pan.
STEP #2 Push the foil into the corners and up the sides of the pan. Try to iron out any wrinkles in the foil, smoothing it flush to the pan. Grease the sides and bottom before adding the batter.
STEP #3 After the brownies, bars, or cakes have baked and cooled, use the foil sling to lift and transfer them to a cutting board before cutting into squares. The foil should easily peel away.
MAKING THE RASPBERRY STREUSEL BARS
STEP #1 Make a simple crust mixture: For an easy, simple crust, we slowly beat softened butter into a mixture of flour and sugar with an electric mixer. The process can take up to 1½ minutes—the final mixture should look like wet sand.
STEP #2 Reserve some crust mixture for the topping: Measure out and reserve 1¼ cups of the mixture to be used later as the base for the streusel topping.
STEP #3 Parbake the crust: Press the crust mixture into the prepared baking pan and bake the crust in a 375-degree oven until the edges begin to brown. Baking the crust on its own (aka parbaking) helps to prevent it from getting soggy when the topping is added.
STEP #4 Turn the crust into streusel: Stir the brown sugar, oats, and nuts into the reserved flour mixture, then work 2 tablespoons more butter into the mixture with your fingers to create hazelnut-sized clumps. The extra butter helps the topping get crispy in the oven.
STEP #5 Make a filling with berries and jam: Mash the jam, raspberries, and lemon juice together with a fork, into small, but noticeable, pieces. Leaving some chunks of berries gives the bars a rustic look and texture.
STEP #6 Add the filling to the hot crust: Using a spatula or butter knife, spread the raspberry filling evenly over the hot crust, then sprinkle with the streusel topping. Spreading the filling over the hot crust allows the filling to cook evenly and prevents the jam from soaking into the crust.