Preheat oven to 425F. Line a 12-cup muffin tin with muffin liners and set aside.
In a large bowl, beat butter and 3/4 cup sugar until smooth and creamy. Beat in eggs and vanilla extract until smooth.
In a separate medium bowl, combine flour, 1 teaspoon cinnamon, baking powder, baking soda, and salt. Add flour in 1/3 increments with buttermilk to butter mixture, folding batter until just combined. Fold in pecans.
In a small bowl, combine remaining 1/4 cup sugar and 1 tablespoon cinnamon.
Fill muffin cups to brim with batter and sprinkle cinnamon sugar over top. Top with a few additional chopped pecans.
Bake muffins at 425F 5 minutes, then reduce heat to 375F and continue baking an additional 10-15 minutes until a toothpick inserted in center of muffin comes out clean.
Cool muffins 20 minutes in pan, then transfer to a wire cooling rack to cool completely. Enjoy!