Raspberry Jam Crumble Bars:

1. Preheat the oven to 350 degrees F. Line a 9×9 or 9×13-inch baking pan with parchment paper, leaving about an inch overhang on two sides. Set aside.
2. In a large mixing bowl, sift together the oats, flour, brown sugar, baking soda and spices until well-combined. Cut the butter into cubes, then use your fingers to incorporate the butter into the dry ingredients, until the mixture is completely moistened, and you’ve formed a shaggy, crumbly dough, that easily sticks together when pinched. This may take a few minutes.
3. Scoop about two thirds of the crumble dough into the baking pan, and press into an even layer along the bottom. Spread the raspberry jam onto the crust, leaving about a 1/4-inch border around the edges. Top with the fresh raspberries, if using, then sprinkle the remaining crumble mixture on top, from edge to edge. Sprinkle with the chopped walnuts.
4. Bake for 30-40 minutes, turning once halfway through, until the jam filling is beginning to bubble and the crumble topping is golden brown and has puffed up a bit. Remove from the oven and let cool completely before cutting into bars.

Quick Vanilla Raspberry Jam:

1. Add the raspberries to a large heavy-bottomed pot. Mash with a wooden spoon to break down the berries. Bring to a full rolling boil, then let boil for a full minute. Add the sugar, stir to combine, and bring back to a boil.
2. Boil for 4-5 minutes, continuing to stir until the sugar is dissolved and a thick gel forms. Remove from the heat and stir in the vanilla and lemon zest (if using). Let cool to room-temperature, then use for the raspberry jam crumble bars, or spoon into air-tight jars to save for later. Will keep for about a week in the refrigerator, or up to a month in the freezer.