Peel and chop the peaches into small pieces. In a medium saucepan, combine the peaches, sugar, cinnamon, and lemon juice. Bring to a boil over medium heat, stirring occasionally. Cook for about 10 minutes until the syrup thickens. Mix the cornstarch with water and add it to the peach mixture, stirring immediately to avoid clumps. Cook for another 2 minutes until thickened. Transfer the jam to a bowl, cover with plastic wrap directly on the surface, and let it cool. Refrigerate for at least 2 hours.

Preheat your oven to 350°F (175°C). In a medium bowl, mix together the flour, granulated sugar, brown sugar, and optional cinnamon. Add the softened butter and use a fork or your hands to mix until crumbly and holds together when pinched. Line a baking sheet with parchment paper, spread the streusel mixture on it, and bake for 10-15 minutes, stirring occasionally, until golden brown. Let it cool.

Grease the sides of your cheesecake pan. Beat the cream cheese with a mixer on medium speed for 3 minutes until creamy. Add the granulated sugar and beat for 2 minutes. Scrape the bowl and beat for another 30 seconds. Mix in the sour cream, scraping the bowl as needed. Add the eggs one at a time, mixing until incorporated. Add the vanilla and salt with the last egg, being careful not to overmix.

Pour about 1½ cups of cheesecake batter into the cooled graham cracker crust. Spoon about ¼ cup of peach jam on top, followed by another cup of batter. Sprinkle ⅓ cup of streusel on top, then cover with another cup of batter. Repeat with another ⅓ to ½ cup of peach jam and the remaining batter, finishing with more streusel on top. Wrap the bottom of the pan with foil and place it in a larger roasting pan. Add hot water to the roasting pan to create a water bath.

Bake in a preheated oven at 325°F (160°C) for 75 minutes. The center should jiggle slightly while the edges are set. Turn off the oven and let the cheesecake rest inside for 1 hour. Remove from the oven and cool before refrigerating for at least 6 hours.

In a chilled bowl, combine the heavy cream, powdered sugar, and vanilla. Whip on medium speed for 1-2 minutes until soft to medium peaks form. Avoid overwhipping.

Once chilled, remove the cheesecake from the pan. Use a cake lifter to transfer it to a serving plate. Pipe the whipped cream around the edge, fill the center with peach jam, and sprinkle with additional streusel if desired.