Preheat oven to 375F.Lightly grease a 10"x15" baking sheet and line with parchment paper. Set aside.For the filling: In a small bowl, add raspberry jam and lemon juice and whisk vigorously until fully combined and smooth. Set aside.Have your whipped cream ready. Set aside in the fridge until ready to use.
In a stand mixer fitted with the whisk attachment, whip the chickpea brine on high until light and foamy - about 2-3 minutes.
Add 6 tablespoons of sugar, one tablespoon at a time to ensure your sugar is well incorporated. Wait 30 seconds or so before you add the next tablespoon and so on.
Continue mixing until your foam is now a beautiful glossy white meringue! Once you achieve this stage, add the lemon juice and whisk 30 seconds more to incorporate it into the meringue. Turn mixer off. Set aside.
In a medium sized bowl, sift together and mix well your dry ingredients: flour, corn starch, baking power, baking soda, salt. Add the remaining 2 tablespoons of sugar and the lemon zest and whisk a few more times to combine.
Then, add the water, oil, and about 1/3 of the meringue to the dry ingredients, and using a spatula, fold the ingredients together until batter is smooth.
Next, add remaining meringue and gently fold into the batter until it's fully incorporated, completely smooth and silky.
Pour and spread the batter onto the lined baking sheet, making sure it's as even as possible (use an offset spatula to help you with this). Tap hard/drop the pan a few times on the counter to remove as many air bubbles as possible. Then place in the preheated oven and bake for 15 minutes.While the cake is baking, have a slightly larger size parchment paper cut and generously dusted with the icing sugar/cornstarch mixture. Set it on the kitchen counter.
Once cake is done, remove from oven, and wait a couple of minutes then flip the cake onto the prepared parchment paper, be swift and careful when flipping! You have to be quick so you don't break the cake since it'll be warm.
Once it's flipped, gently remove the parchment paper on top and discard, then allow it to cool slightly, about 15 minutes, until it's at room temperature when touched. Slightly warm is ok.
Spread the jam all over the cake, followed by the whipped cream, leave about an inch from the end of the cake away from you. Sprinkle the raspberry pieces all over the whipped cream, crushing the berries in your hand as you go.
Taking the ends of the parchment paper, using them as guide, gently start folding your cake, try to make it a tight roll. The tighter the more structure your cake will have and the prettier it will look.
Trim excess parchment paper, and use a plastic wrap to wrap the cake tightly once again, and shape and smooth the cake with your hands once the cake is wrapped.Place in the fridge and allow it to set.
When ready to serve, remove the cake from the fridge, remove the plastic wrap and carefully peel the parchment paper off. Set it on desired serving plate, dust generously with icing sugar, cut into even pieces, and enjoy!!