Toast pecans. Combine boiling water and oats in a medium bowl. Set aside to cool, about 20 minutes.
Grease and flour a 9 x 13 cake pan. (Or use non-stick spray with flour.) (You can also bake the cake in half size or full-size bundt pans.)
In a medium bowl, whisk together flour, baking soda, cinnamon, salt, and nutmeg. Set aside.
In a large mixing bowl, beat granulated sugar, brown sugar, butter, and vanilla at medium speed for 5 minutes. Add eggs, 1 at a time, beating well after each addition. Add oatmeal, and beat until blended. Add sour cream and mix on low until blended. Add flour mixture and mix until well combined. Stir in raisins and ¾ cup chopped pecans. (¼ cup is reserved for decorating the top of the cake.)
Pour the mixture into the prepared pan(s). Bake about 40 minutes (half size Bundt for 35 minutes; full-size Bundt for 50-60 minutes) until a toothpick comes out clean.
Let cool completely before making the icing.
Caramel Icing
In a small saucepan, combine butter, brown sugar and cream. Bring to a boil over medium heat, stirring occasionally. Cook 3 minutes; stirring constantly. Remove from heat and gradually whisk in powder sugar and vanilla. Whisk until smooth adding more cream or powdered sugar as needed to make a thin icing. (Icing will thicken as it cools.)
Drizzle the hot icing on top of the cake. Sprinkle with remaining ¼ cup chopped pecans. Store the cake loosely covered in refrigerator.
Notes
*To toast pecans: In a small heavy skillet, melt 2 tablespoons butter. Add pecans; cook over medium heat until toasted, about 4 minutes. Set aside to cool.High altitude adjustment: Increase oven to 375º. Reduce granulated and brown sugar to ⅔ cup. Bake for 30 minutes.