Step 1: Preheat your oven to 350°F (175°C). Wrap the bottom and sides of a 9-inch springform pan tightly with heavy-duty aluminum foil to prevent water from seeping in during the water bath.
Step 2: For the crust, combine graham cracker crumbs, 1/4 cup granulated sugar, and 6 tablespoons melted butter in a medium bowl. Press the mixture firmly into the bottom of the prepared springform pan. Bake for 10 minutes, then remove from oven and let cool slightly.
Step 3: Reduce oven temperature to 325°F (160°C).
Step 4: In a large mixing bowl, beat softened cream cheese with 1 1/2 cups granulated sugar until smooth and creamy, about 3-4 minutes. Scrape down the sides of the bowl as needed.
Step 5: Mix in the flour and vanilla extract until just combined. Stir in the sour cream.
Step 6: Add eggs one at a time, beating on low speed just until each egg is incorporated. Do not overmix.
Step 7: In a small bowl, combine the brown sugar, cinnamon, and 2 tablespoons melted butter for the cinnamon swirl mixture.
Step 8: Pour about half of the cheesecake batter over the cooled crust. Dollop half of the cinnamon swirl mixture over the batter. Gently swirl with a knife or skewer.
Step 9: Pour the remaining cheesecake batter over the swirl layer, then dollop the remaining cinnamon mixture on top. Swirl again gently.
Step 10: Place the springform pan in a larger roasting pan. Carefully pour hot water into the roasting pan until it reaches about halfway up the sides of the springform pan.
Step 11: Bake for 1 hour 15 minutes, or until the edges are set and the center jiggles only slightly when gently shaken. Turn off the oven, crack the oven door, and let the cheesecake cool in the water bath for 1 hour.
Step 12: Remove the cheesecake from the water bath and aluminum foil. Let it cool completely on a wire rack at room temperature. Once cooled, cover and refrigerate for at least 4-6 hours, or preferably overnight, to chill thoroughly.
Step 13: For the cream cheese icing, beat softened cream cheese and 1/4 cup softened butter together until smooth. Gradually add powdered sugar, mixing until well combined. Beat in milk/cream (start with 1 tablespoon and add more if needed for desired consistency) and vanilla extract until light and fluffy.
Step 14: Spread the cream cheese icing over the chilled cheesecake before serving. Enjoy!