Heat oven to 350°F. Butter a 9x13-inch baking dish.
Simmer melted butter, brown sugar, heavy cream, cinnamon, vanilla, and salt in a small saucepan for 2 minutes, stirring until smooth.
Pour about half of the sauce into the dish and scatter half of the pecans over it.
Slice the slab of rolls horizontally to make a top and bottom. Set the top aside.
Nestle the bottom half in the dish. Spoon a few tablespoons of sauce over the cut side.
Replace the top half. Pour the remaining sauce over and around the rolls. Sprinkle on remaining pecans and raisins, if using.
Bake until deeply golden and bubbling at the edges, 18–22 minutes.
Cool 5 minutes. Run a knife around edges, invert onto a platter, and spoon any sauce from the pan over the buns. Serve warm.