Place the blackberries, the sugar, and the lemon juice in a medium saucepan. Cook the blackberries over medium heat, stirring every so often, for about 10 minutes. Press the blackberries against the side of the pan to help crushing them.

If the mixture is drying and sticking to the bottom of the pan, add one tablespoon of water, or more as needed.

Mix the cornstarch and water together until the cornstarch has dissolved.

Once the blackberries have dissolved and the mixture is thick and syrupy, add the dissolved cornstarch to the pan and immediately mix with a spatula. Cook for 2 minutes, stirring, until the sauce is thick.

Remove the sauce from the heat, and pour into a fine-mesh strainer over a bowl, to retain the seeds and the core of the blackberries. Press the blackberries down in order to obtain as much sauce as possible. Scrape the bottom of the strainer because a lot of the jam will accumulate there.

You should obtain 1 cup of sauce. Reserve two tablespoons for the whipped cream, keep it covered so it doesn't form a skin. The rest will be swirled into the cheesecake batter.

If you don't have one cup of sauce, return the blackberry pulp to the saucepan, add one or two tablespoons of water and gently re-heat. Then pass it through the sieve again, to obtain more jam.

Pre-heat the oven to 325ºF.

Place the graham cracker in a food processor and process to obtain fine crumbs.

Add the brown sugar and mix to combine.

Melt the butter and mix with the crumbs and sugar.

Press the mixture on the bottom of an 8” or 9” cheesecake pan. If using an 8” springform pan, it must be deep.

Bake the crust in the oven for 10 minutes.

Remove it from the oven and let it cool down.

Grease the sides of the cheesecake pan.

Beat the cream cheese for 3 minutes with a mixer at medium speed, until creamy.

Add the granulated sugar to the bowl and beat for 2 minutes at medium speed.

Scrape the bowl and beat for another 30 seconds.

Add the sour cream and mix to combine. Scrape the bowl.

Add the eggs one at a time to the bowl, mixing until incorporated before adding the next one.

Along with the last egg, add the vanilla and the salt.

Pour one third of the cheesecake batter on the bottom of the baked and cooled graham cracker crust.

Add about one third of the blackberry sauce in spoonfuls on top of the batter.

Use a knife or a spatula to swirl the sauce into the cheesecake batter gently.

Pour another third of the cheesecake batter on top of the swirled batter and sauce.

Pour another third of the blackberry sauce in spoonfuls on top of the batter. Swirl it gently with a spatula or knife.

Pour the remaining cheesecake batter on top, and top with the remaining blackberry sauce. Swirl it around with a spatula.

Wrap the bottom of the pan with a few layers of foil.

Place the pan in a larger roasting pan, and add hot water to the roasting pan, to form a water bath.

Bake the cheesecake in the pre-heated 325ºF oven for 60 to 75 minutes.

To check if the cheesecake is done baking, give the pan a little wiggle, it should jiggle slightly in the center, but the edges should look set.

Turn the oven off, and leave the cheesecake in there for 1 hour.

Remove the cheesecake from the oven, let it cool down. Don’t remove the ring of the pan yet, place the cheesecake in the fridge to chill for at least 6 hours.

To a large bowl, add the heavy cream, powdered sugar, and blackberry jam.

Whip with the whisk attachment for about 3 minutes, or until the cream achieves stiff peaks.

Place it in a piping bag fitted with the tip of choice.

After the cheesecake has been done chilling, remove from the fridge. Remove the ring from around the pan.

You can use a cake lifter tool to lift the cheesecake from the pan and slide it onto a serving plate.

Pipe the whipped cream on top of the cheesecake and decorate with fresh blackberries if desired.