Preheat oven to 350°. Lightly grease 9-inch springform pan with cooking spray and set aside.
In a large bowl whisk together flour, baking soda, pumpkin pie spice, cinnamon, and salt.
In a medium bowl, whisk together walnut oil, brown sugar, eggs, and vanilla extract until combined.
Pour wet ingredients into the dry ingredients and fold in until combined (do not overmix).
Fold in the pumpkin puree and incorporate well.
In a medium bowl, using an electric mixer on high speed beat together quark, powdered sugar, eggs, and flour until smooth. Add vanilla extract and mix until blended. Spread half of the pumpkin cake batter into the bottom of the prepared springform pan. Dollop half of the quark cheesecake batter on top of the pumpkin cake layer in a large spoonful, don’t spread or swirl together, (let gravity do the work).
Dollop the rest of the pumpkin cake batter on or around the spoonful of cheesecake batter without spreading or swirling, then pour in the rest of the batter on top.
Bake for about 50-60 minutes in total. Check-in on the cheesecake halfway through to see if it’s browning too quickly. If so, tenting the top of the cheesecake with foil will prevent it from browning anymore.
The cheesecake will puff in the oven and might even crack, but we’re not going for perfection here, just a really simple, kind of rustic cheesecake look.
Remove from oven and allow to cool completely but do not remove from the springform. Refrigerate overnight (in the springform). When ready to serve, remove from the pan and lightly dust the top with powdered sugar.
The cheesecake stays fresh for about 3 days, covered.