For the muffins: Preheat oven to 400 degrees. Generously grease 12 muffin tins. Sift the flour, sugar, baking powder, cinnamon, ginger, nutmeg, and salt. Cut in the butter with two knives or a pastry blender until it is fully incorporated. In a separate bowl, mix together the pumpkin puree, evaporated milk, egg, and vanilla. Pour the pumpkin mixture into the flour mixture. Add the raisins, if using. Fold gently until the mixture is just combined.  Pour into the greased muffin tin- the batter hardly ever fills all twelve unless you keep it down to 1/2 full.  For the topping- in a small bowl, combine the sugar, cinnamon and nutmeg. Sprinkle all over the top of each unbaked muffin. Bake for 20-25 minutes, until golden brown. Allow to cool in pan for 10 minutes, then remove and allow to cool completely. Ice with cream cheese frosting, if desired. For the frosting: Combine the butter, cream cheese, powdered sugar and vanilla in the bowl of an electric mixer. Mix all ingredients on high until soft and whipped. Spread onto completely cooled muffins, or place into a large pastry bag with a large star tip and go crazy! Store in the fridge, as icing will soften at room temperature.