Make the topping: Preheat oven to 425F. Bring butter and sugar to a low simmer over medium-high heat. Stirring occasionally, cook caramel until a deep golden brown and slightly thickened. Remove from heat and whisk in whipping cream and a pinch of salt. Divide chopped pecans between a greased 12-cup muffin tin, placing nuts in the bottom. Top each with about 1/2 to 1 tablespoon caramel sauce. Set aside.
Make the muffins: In a large bowl, whisk pumpkin, sugar, eggs, oil, buttermilk, and vanilla until smooth. In a separate bowl, combine flour, baking powder, salt, and pumpkin pie spice. Gently fold flour mixture into liquid, stirring until just combined.
Divide muffin batter evenly between muffin cups, carefully spooning batter over nuts and caramel. Smooth tops. Bake muffins at 425F 5 minutes, then reduce heat to 375F and continue baking 15-16 minutes or until a toothpick tests done.
Cool muffin in pan 5-10 minutes, then very carefully, run a knife around muffins and quickly invert onto a cooling rack. Enjoy muffins warm!
Store muffins in an airtight container at room temperature up to 2 days.