Cream butter; gradually add 3/4 cup sugar, beating well. Add sweet potatoes and eggs, beating well.
Combine flour, baking powder, 1 teaspoon cinnamon, nutmeg, and salt. Add flour mixture to creamed mixture alternately with milk, beginning and ending with flour mixture. Stir in raisins and pecans.
Spoon batter into greased miniature muffin pans, filling two-thirds full. Combine 1/4 cup sugar and 1/2 teaspoon cinnamon; sprinkle evenly over each muffin. Bake at 400° for 25 to 30 minutes.