Preheat the oven to 350°F / 175°C. Butter a 7" springform pan, then coat the inside with sugar.
To a medium sized mixing bowl, add the flour, pistachio flour, baking powder, salt, sugar, and cubed butter. Use a hand mixer or a stand mixer fitted with the paddle attachment to beat the mixture together until the butter has completely combined with the dry ingredients and no lumps remain.
Add in the oil, egg whites, vanilla, sour cream, and milk. Whisk the ingredients together just until a cohesive batter has formed.
Pour the cake batter into your prepared pan. Bake for 35-45 minutes, until a toothpick inserted in the center of the cake comes out with only a few moist crumbs.
While the cake is baking, work on the raspberry jam, pistachio mascarpone whipped cream, and the pistachio milk soak.
Raspberry Jam
Set a fine mesh sieve over a small bowl. Set aside.
Add the raspberries, lemon zest, 15g (1 tbsp.) of lemon juice, and the sugar to a small saucepan set over medium heat. Stir the mixture frequently, mashing down the raspberries as they soften.
Once all the raspberries have been mashed up, take the mixture off of the heat and pour it through the fine mesh sieve.
Press down on the raspberries to get out as much of the juice as possible. Discard the raspberry seeds, and transfer the mixture back into the saucepan and bring it to a simmer.
In a small bowl, mix together the corn starch and remaining lemon juice. Once the raspberry mixture is simmering, mix the corn starch slurry in to it, stirring until the jam thickens.
Once thickened, remove the jam from the heat and transfer it to a heat-safe container to chill in the fridge until you're ready to assemble the cake.
Pistachio Mascarpone Whipped Cream
Add the mascarpone, sugar, pistachio cream, salt, and vanilla to a medium sized mixing bowl. Use a hand mixer (or a stand mixer fitted with the whisk attachment) to beat the mixture just until combined.
While mixing, slowly pour in the heavy whipping cream. Continue mixing until the mixture reaches stiff peaks.
Cover the cream and place it in the fridge until you're ready to assemble the cake.
Pistachio Milk Soak
Add the pistachio cream to a small mixing bowl.
In a small microwave-safe measuring cup, heat the milk until it just starts to bubble up. Pour the milk over the pistachio cream and mix until well combined.
Cover the mixture and place it in the fridge until you're ready to assemble the cake.
Assembly
Once the cake has completely cooled to room temperature, slice it in half horizontally twice to get three even pieces.
Place the bottom piece of the cake back into your springform pan. Brush ⅓ of the pistachio milk over the cake, then top it with ⅓ of the pistachio mascarpone and ½ of the raspberry jam.
Place the middle layer of cake on top, then top it with ½ of the remaining pistachio mascarpone and the remaining raspberry jam.
Brush the remaining pistachio milk over the bottom of the top layer of cake, then place the top layer of cake on to the cake. Cover the cake and place it in the fridge for 30 minutes to firm up.
Once you're ready to serve the cake top it with the remaining pistachio mascarpone and fresh raspberries. Slice, serve, and enjoy!