To make the jam:Place a big metal bowl or baking dish in the freezer to chill. This will help cool down the jam quickly later. If you prefer, you can avoid this step by making the jam the night before, just bring it up to room temperature before baking the cake the next day.

In a small saucepan, combine the blackberries, sugar, lemon juice, and salt. Heat over medium heat and bring to a simmer. 

Once simmering, cook the berries until very soft and begin to fall apart, stirring occasionally to prevent scorching. Turn down the heat if the mixture starts bubbling too aggressively. 

While the berries are bubbling, mash the fruit with a fork or spatula to break down any big pieces of blackberry. Simmer until no big chunks of fruit remain and the syrup is thick, coats the back of a spoon, and has reduced to 1 cup, about 11-15 minutes total of simmering.

Remove the jam from the heat and pour into the chilled bowl/dish. Pop the jam in the fridge to cool down completely while you make the cake. 

To make the cake:Preheat the oven to 350° and grease and flour a 9” springform pan. Set aside.

Combine the cake flour, baking powder, and salt in a small bowl. Give the dry ingredients a mix with a whisk or fork and set aside.

In the bowl of a stand mixer, add the butter. With the paddle attachment, beat the butter for 30 seconds on low speed to smooth. 

Add the vegetable oil and sugar and beat on medium high speed until very light in color and fluffy, about 2 minutes. Stop the mixer and use a rubber spatula to give the sides and bottom of the bowl a scrape.

Turn the mixer to low speed and add the eggs one at a time, mixing completely before adding the next egg. 

Once all the eggs have been incorporated, stop the mixer, give the bowl another scrape with the spatula, and add the lemon zest, juice, and vanilla. Mix on low until fully incorporated. If the mixture looks a bit curdled that’s totally fine.

Next, alternate adding the dry and wet ingredients. With the mixer on low, start by adding half of the flour mixture to the mixing bowl. Mix until almost combined and then pour in all of the milk. Stir until halfway mixed and then add the last of the flour mixture.

Stir on low until almost fully combined, then turn off the mixer and give the mixing bowl a final scrape with a rubber spatula. Turn the mixer back on and turn up to medium speed. Mix until the batter is fully combined and fluffy, about 20-30 seconds.

Grab the prepped springform pan and spoon about 2/3 of the cake batter into the pan. Use a spatula to gently smooth into an even layer.

Next, take the blackberry jam out of the fridge or freezer and make sure it’s cooled to room temperature.

Using about 2/3 of the blackberry jam, spoon little dollops over the top of the cake batter. Do not smooth out the jam.

Next, spoon the remaining third of the cake batter over the jam dollops and lightly smooth out the top of the batter into an even layer. Do your best not to disturb the jam dollops underneath, we’re not trying to stir them together.

Drop the last of the jam over the top of the cake batter in spoonfuls.

Next, take a butter knife and insert it into the cake batter. Drag the knife across the pan from left to right and then from top to bottom to make swirls. Do not stir.

Pop the cake in the oven and bake for 45-60* minutes until the cake is golden brown, risen, and a toothpick inserted has come out clean.

Once baked, remove the cake from the oven and set it on a cooling rack.

After about 10 minutes of cooling, run a thin knife between the cake and the edge of the pan to loosen. Release the sides of the springform pan and allow the cake to finish cooling. Once the cake is cool enough to handle, you can remove the bottom of the springform pan if you choose.

While the cake is cooling, make the whipped creamIn the bowl of a stand mixer, fitted with the whisk attachment, add the heavy cream, sugar, lemon zest and lemon juice. 

Stir on low speed for 10-15 seconds to combine and then turn the speed up to medium high and whip until stiff peaks have formed, about 30-60 seconds. 

You’ll know the cream is ready when you remove the beater from the bowl and the cream stands on the end of the whisk without drooping or running off.

You can serve this cream on the side if the cake is still warm (highly recommended) or pile the cream on top of the cake after it has cooled completely. Garnish with fresh blackberries and enjoy.