Preheat the oven and prep the pan – Set oven to 325°F (160°C) and grease or line a 9-inch springform pan.
Make the crust – Mix graham cracker crumbs, sugar, and melted butter; press into pan base.
Bake the crust – Bake for 10 minutes, then cool slightly.
Prepare the cinnamon filling – Mix flour, sugar, butter, cinnamon, milk, and egg until smooth.
Add cinnamon swirl – Spoon and swirl the cinnamon mixture over the crust.
Make cheesecake filling – Beat cream cheese, gradually mix in sugar, then eggs, sour cream, and vanilla.
Assemble – Pour cheesecake mixture over the cinnamon layer and smooth the top.
Bake – Bake for 55–60 minutes until just set; leave in oven with door ajar for 15 minutes.
Cool – Cool on a wire rack for 1 hour, then chill in the fridge for at least 4 hours or overnight.
Make frosting – Beat cream cheese and butter, mix in powdered sugar, milk, and vanilla.
Frost and serve – Spread frosting over the chilled cheesecake, slice, and enjoy.