Preheat oven to 350°F (175°C). Wrap the bottom and sides of a 9-inch springform pan with several layers of heavy-duty tinfoil to prevent water leaks. Spray the pan with non-stick spray.

Pulse 1/2 cup pecans in a food processor until they become fine crumbs. Combine pecan crumbs, graham cracker crumbs, 1/3 cup granulated sugar, 1/4 tsp cinnamon, 1/4 tsp salt, and melted butter in a bowl. Press the mixture firmly into the pan and up the sides to form an even crust.

Bake the crust for 10 minutes. Remove and cool on a rack. Reduce oven to 325°F (163°C).

Beat the soft cream cheese with the sour cream until smooth and lump-free. Add 1/2 cup dark brown sugar, 2/3 cup granulated sugar, 1/4 tsp cinnamon, and 2 tsp vanilla. Beat on medium until combined and smooth.

Lower mixer speed. Add the 3 whole eggs and 2 yolks one at a time, mixing briefly after each addition. Avoid overbeating; stop as soon as each egg is incorporated.

Fold in 1 tbsp bourbon (if using) and 2 tbsp flour by hand with a spatula. Scrape the batter over the cooled crust and smooth the top.

Place the springform pan inside a large roasting pan. Pour in hot water to reach about 2 inches up the outside of the springform. Bake at 325°F (163°C) for 1 hour and 10 minutes. The center should be slightly jiggly but not liquid.

Turn off the oven and let the cheesecake sit inside with the door closed for 30 minutes to finish gently.

Run a thin knife around the edges to loosen. Cool completely on a wire rack, then chill the cheesecake in the refrigerator for at least 8 hours (overnight is best).

In a skillet, melt 6 tbsp butter with 2/3 cup dark brown sugar until it bubbles. Whisk in 1/2 tsp cinnamon, 1/3 cup heavy cream, and 1/4 tsp salt. Fold in 2 cups pecans.

Remove from heat and stir in 1 tsp vanilla and 1 tbsp bourbon (optional). Cool the topping about 10 minutes, then spoon over the chilled cheesecake.

Slice and serve.