170g1 1/2 sticks unsalted butter, cut into 1-inch pieces
For the raspberry filling:
1/4cupfirmly packed dark brown sugar
1tablespoongrated lemon zest
1teaspooncinnamon
2tablespoonsall-purpose flour
500g1lb raspberries, fresh or 600g frozen
1/4cupfresh lemon juice
30g2 tablespoons unsalted butter, melted and cooled
Instructions
Make the crust and crumb: Preheat the oven to 350°F. Butter the bottom and sides of a 31x 21 cm (9-by-13-inch) glass or light-colored metal baking pan. Line the pan with a piece of parchment paper, cut to hang over the short sides of the pan to allow easy removal of the bars.
Place the flour, brown sugar, oats, salt, baking powder, baking soda, and cinnamon in a food processor. Pulse until combined. Add the butter and pulse until a loose crumbs forms.
Reserve 1-1/2 cup of the mixture and set aside. Place the rest of the mixture into the prepared pan and press the crumb mixture evenly in the pan with the back of a large wooden spoon. The crust should touch the sides of the pan. Bake until golden brown, 12 to 15 minutes. Transfer the pan to a wire rack and cool. Keep the oven on while you prepare the raspberry filling.
In a medium bowl, whisk the sugar, lemon zest, cinnamon and flour together. Add the raspberries, lemon juice and butter and toss gently with your hands until the raspberries are evenly coated.
Gently place the raspberry filling evenly on top of the cooled crust. Sprinkle the reserved crust mixture evenly on top of the filling.
Bake for 35 to 45 minutes until the top is golden brown and the filling starts to bubble around the edges.
Transfer to a wire rack to cool completely, then cut into squares and serve. The bars can be store in the refrigerator in an airtight container for up to two days.