In a baking pan toast pecans in one layer in middle of oven until golden, about 10 minutes, and cool.

In a food processor finely grind pecans, wafers, and graham crackers.

Add brown sugar, butter, and salt and pulse until combined well. 

Transfer mixture to a 9- and- 1/2-inch springform pan and press evenly onto the bottom and 1 and 1/2 inches up the side.

Preheat oven to 350°F.

In a bowl with an electric mixer beat cream cheese until fluffy and add eggs, one at a time, beating at low speed until just combined.

Beat in bourbon, vanilla extract and brown sugar until just combined.

Pour filling into crust and put springform pan inside a baking pan. Bake cheesecake in middle of oven 35 minutes. Leaving oven on, transfer cake in springform pan to a rack and let stand five minutes. (Center of cake will set as it cools.)

In a bowl stir together sour cream, brown sugar, and vanilla extract. Drop spoonfuls of topping around edge of cake and spread gently over center, smoothing evenly.

Bake cake in baking pan in middle of oven 10 minutes and cool completely in spring form pan on rack. Chill cake, covered, at least 8 hours and up to 4 days.

Run a thin knife around inside edge of pan and remove side of pan. Transfer cake to a serving plate and let stand at room temperature 30 minutes. Serve cake with sauce (below).

In a dry 3-quart heavy kettle cook sugar over moderately low heat, stirring slowly with a fork (to help sugar melt evenly), until melted and pale golden. Cook caramel, without stirring, swirling kettle, until deep golden.

Remove kettle from heat and carefully add water and bourbon down side of kettle (mixture will bubble and steam). 

Simmer mixture, stirring, until caramel is dissolved.

Stir in butter until incorporated and cool sauce to warm.