Prepare:
Preheat oven to 350°F.
Prepare a 7x11 inch baking pan (optionally line with parchment paper, leaving overhang for easy removal).
Make the Crust:
Melt butter and mix with 4 tablespoons sugar in a medium bowl until sugar dissolves.
Add graham cracker crumbs and mix until mixture resembles wet sand and all crumbs are coated.
Press mixture firmly into the bottom of prepared pan using the bottom of a measuring cup to compress well. Set aside.
Make the Filling:
In a mixing bowl, beat cream cheese and sour cream together on medium speed for about 1 minute until light and fluffy.
Add 3/4 cup sugar gradually, mixing until completely smooth.
Add eggs one at a time, beating well after each addition and scraping down sides of bowl between additions.
Pour in vanilla extract and mix just until combined (avoid overmixing).
Pour filling over crust and spread evenly, reaching all corners. Tap pan gently on counter to release air bubbles.
Bake:
Bake for 25 minutes until edges are set and center still jiggles slightly like Jell-O (internal temperature should reach 150°F).
Turn off oven, crack door open slightly, and let cheesecake cool inside for 30 minutes to 1 hour.
Remove from oven and cool completely on a cooling rack (30-45 minutes).
Cover with plastic wrap and refrigerate for minimum 2 hours (overnight is best).
Make the Chai Whipped Cream:
In a chilled bowl, beat cold heavy cream on medium-high speed for 2-3 minutes until soft peaks form.
Add chai powder and 2 tablespoons powdered sugar. Continue beating until stiff peaks form (1-2 minutes more). Taste and add more sugar if desired.
Assemble:
Spread chai whipped cream over chilled cheesecake bars.
Optional: Dust with cinnamon using a fine-mesh sieve.
Cut into 12-16 bars using a sharp knife, wiping clean between cuts for neat edges.
Serve slightly chilled or at room temperature (remove from fridge 10-15 minutes before serving for best flavor).