Preheat oven to 350°F. Lightly grease 24 standard muffin cups.
In a small bowl, mix together melted butter, brown sugar and corn syrup. Spoon a teaspoon of this caramel mixture into prepared muffin cups. Sprinkle a tablespoon of pecans on top of caramel in each cup. Set aside.
In a large bowl, whisk together flour, sugar, baking soda, pumpkin pie spice and salt . Set aside.
In a medium bowl, whisk together pumpkin, oil, eggs, buttermilk and vanilla. Make a well in the middle of the dry ingredients and pour in wet mixture. Stir until just combined. Divide batter evenly among the muffin pans, covering the caramel topping and filling each cup about 3/4 full.
Bake at 350°F for 18 to 20 minutes or until a toothpick inserted into the center comes out clean. You may wish to place a cookie sheet or foil on the rack below pans, to catch any of the topping that may bubble over. Remove muffins from oven, and immediately invert each pan over a cookie sheet or large serving platter. Scoop any of the remaining topping onto the muffins. Cool for five minutes and serve.
These muffins taste best warm. You may keep in an airtight container for up to three days.