How to Make It
Preheat the oven to 350º. In a food processor, pulse the almond flour, melted butter, sugar, salt and baking powder until incorporated but still coarse.
Line a nonstick 9-by-9-inch baking pan with parchment paper, leaving at least 1 inch overlapping the sides (for removal later). Press the crust into the pan and bake for 10 minutes.
In a small saucepan, combine the raspberries, vanilla extract, syrup and lemon zest and bring to a boil. Remove from heat and set aside. Remove the partially baked crust from oven and let it cool for 10 minutes.
Combine the walnuts, almond flour, brown sugar and butter in a bowl and set aside.
Once the crust has cooled, spread with the raspberry filling and sprinkle with the streusel topping. Bake for 20 minutes, or until the topping turns golden brown. Remove from the oven and allow to cool for 30 minutes. Use the overlapping parchment paper to carefully remove from the pan. Slice the bars into squares and serve.