Preheat the oven to 325 degrees F. Spread the pecans on a baking sheet. Bake until toasted, about 8 minutes. Let cool, then chop.
Coat a 9-inch square baking dish with cooking spray. Line with parchment paper, leaving an overhang; coat the parchment with cooking spray.
Make the cheesecake batter: Beat the cream cheese and granulated sugar in a large bowl with a mixer on medium speed until creamy, about 3 minutes. Beat in 1 egg and 1/2 teaspoon vanilla until combined; set aside.
Make the blondie batter: Whisk the flour, baking powder and fine salt in a medium bowl. Whisk the melted butter and brown sugar in a large bowl; whisk in the remaining 2 eggs and 1 teaspoon vanilla until combined. Fold in the flour mixture with a rubber spatula until just combined. Stir in 3/4 cup pecans.
Spread half of the blondie batter in the prepared pan. Top with half of the cheesecake batter in spoonfuls. Warm the caramel sauce in the microwave, then drizzle between the spoonfuls of cheesecake batter. Top with the remaining blondie batter, then the remaining cheesecake batter in spoonfuls. Using the tip of a butter knife, gently swirl together to create a marbled effect.
Bake until a toothpick inserted into the center comes out clean, 50 to 55 minutes. Let cool 10 minutes in the pan, then lift the blondies out of the pan using the parchment and transfer to a rack. Drizzle with more caramel sauce and sprinkle with the remaining 1/4 cup pecans and the fleur de sel. Refrigerate until completely cooled, about 2 hours. Cut into squares.
Photograph by Ryan Dausch