About 1/2 cup of berry pureeadd more on top if you wish or save some for individual servings
In a sauce pot, over medium heat, combine all berries, sugar, and lemon juice. Stir and let it cook, uncovered. Make sure to stir every few minutes. Let the berries simmer for about 20 minutes, some of the liquid will cook down.
Take the sauce pot off heat and puree the mixture either with an immersion blender or in a separate blender. Set aside.
Preheat the oven to 325 and grease a 9 inch spring form. You will need a large roasting pan (one that’s bigger and longer than the spring form. I use the aluminum foil disposable roasting pan.)
In a small bowl, combine graham cracker crumbs, melted butter, vanilla extract and brown sugar. Mix very well.
Spread crumb mixture in the bottom on the spring form, evenly, pressing it over the bottom and about half way up the sides.
Spread 1/3 cup of berry puree evenly over the crust.
In a bowl of an electric mixer, beat cream cheese on medium-high speed until smooth and fluffy. Scrape sides and bottom on the bowl and beat for another minute.
Add corn starch and sugar and mix until combined.
Beat in eggs, one at a time, until well incorporated.
Add sour cream, vanilla extract, and heavy cream, and beat until all mixed very well.
Drop scoops of cheesecake batter all over the crust, covering it completely and then even it out. (If you just pour in the batter, it will start mixing with berry puree.)
(If you are not sure about your springform holding up in water, you can wrap the springform in heavy duty aluminum foil from bottom up to the sides, pressing it tight to the outside of the springform.)
Place roasting pan into the oven and place cheesecake springform inside the roasting pan. Carefully add water to the roasting pan, about half way up the side of the spring form.
Bake for 85-90 minutes. Turn off the oven and open the oven door half way. Let cheesecake rest for 10 minutes and take it out of the oven (out of the water bath).
Let it rest for 10-15 minutes on the counter and then gently run a greased butter knife between sides of the cheesecakes and the springform to carefully separate it. (You don't actually have to take the cheesecake out of the pan until ready to add toppings.) Let it cool to the room temperature before covering and putting it in the fridge.
Refrigerate the cheesecake for at least 6 hours or overnight. (You can transfer the berry puree into a glass jar until ready to use.)
When ready to serve the cheesecake, take the side rim of the springform off. Pour 1/2 cup of berry puree on top of the cheesecake, in the center. Gently spread it with a spatula over the top. Then, add berries. It's easier to place strawberries first and then add blueberries and raspberries.
If you will have leftover, just put the side rim of the springform back on and cover it with a saran wrap over the top.