Preheat oven to 375. Line baking sheet with parchment paper and wrap the outside of a 10 inch springform pan with foil. Toss the pecans with 1/2 teaspoon of butter, 1/2 tablespoon sugar, the brown sugar, cream and salt in a bowl. Spread the nuts on baking sheet. Bake for 18 minutes, until sugar is caramelized and pecans are toasted. Let cool.Put all but 12 of the pecans in a food processor along with the graham crackers. Pulse until fine. Add the remaining melted butter and 1/3 cup of sugar and pulse until crumbs are moistened. Press crumbs over bottom and 2/3 up the sides of the prepared pan. To make the filling, in a clean processor, pulse the cream cheese and sugar until smooth. Add the eggs, one at a time, pulse unti mixed. Pulse in vanilla and sour cream then scrape filling into the prepared pan. Bake for about an hour or until the top of the cheesecake is lightly golden in spots and center is slightly jiggly. Transfer cheesecake to a rack and let it cool completely. Wrap it in plastic and refrigerate it overnight. To make the sauce, in a pan, mix the butter with all the sugars and bring to a boil. Stir constantly. Add the cream. Boil for 2 minutes. Transfer to pitcher. Stir in the vanilla and salt and refrigerate until cold, at least 2 hours or overnight. Unwrap cheesecake and discard foil. Remove ring and transfer cake to a plate. Arrange 12 reserved pecans on top. Using a warm slightly moistened knife, cut cake into wedges, wiping and rewetting the blade between slices. Transfer to plates and pour some of the caramel sauce on top. Pass remaining sauce.