In a saucepan, warm the heavy cream over medium heat. When hot, add the tea bags, pressing down to submerge. When the cream is hot but before it begins to boil, remove from the heat. Cover and let steep for at least 30 minutes.
After steeping, remove the tea bags. Squeeze the tea bags well to reserve as much of the cream as you can. Strain the cream into a measuring cup. Add more cream if needed to ensure there is at least 1 1/2 cups cream.
In a stand mixer, combine the softened cream cheese and sugar. Cream on low with a paddle attachment until smooth. Scrape down the sides of the bowl as needed.
Add the eggs one at a time, beating on low just until combined, scraping the bowl as needed. Add the vanilla paste and the earl grey steeped cream. Mix on low just until combined. Sift the flour and then add to the mixer. Mix on low just until the flour is fully combined.
Preheat the oven to 425°F. Cut two large squares of parchment paper to line a 9" springform pan making sure they come up 2 inches past the top. Scrunch the parchment paper and then smooth out. Overlap the two papers in the pan, pressing evenly into the pan. The edges will be crinkled. Spray lightly with non-stick spray.
Pour the batter into the parchment lined pan. Bake for 50 to 60 minutes until the top of the cheesecake is well browned. The cheesecake should still be jiggly in the middle but not runny. Remove from the oven and let cool for at least 4 hours before serving.
Blackberry Sauce
Blend the blackberries in a food processor. Pour the berries into a fine mesh strainer over a bowl. Using a spatula, work the blended berries through the strainer until only the seeds are left. Scrape any excess purée from the bottom of the strainer, then transfer the purée to a small saucepan and discard the seeds.
In a separate bowl, whisk together the sugar and cornstarch. Whisk the dry ingredients into the blackberry purée along with the lemon juice and turn the heat to medium low. Cook, whisking constantly, until the purée begins to bubble and thicken.
Remove from the heat. Add the cassis, if using. Pour the filling into a bowl and cover with a piece of cling film. Chill until ready to serve.
To Serve
This cheesecake is best served the same day it's baked, after cooling for 4 to 6 hours. It can be chilled overnight in the fridge, however the texture will be firmer. To serve, remove the outer ring from the pan. Carefully peel the parchment off the sides of the cheesecake. Use a hot knife to cut the cheesecake into slices. Top each slice with the blackberry sauce and fresh blackberries. Enjoy!