Pierce each potato twice with point of sharp knife to vent stem. Place in single layer in microwave oven. Microwave on high 5 minutes. If potatoes are not cooked through, turn potatoes over and continue mirowaving 1 minute at time until softened. Remove any fully cooked potatoes from microwave while cooking remaining potatoes. Cool potatoes 10 minutes
In a small bowl mix flour, brown sugar, 2 TBSP butter and with pecans, set aside.
Heat oven to 350 degrees, cut off top 1/3 of each potato. Using a spoon, scoop flesh into large bowl, being careful not to tear potato skins, discard potato tops. Add 2 TBSP butter, half and half, spice, and slat to potatoes. Mash potato mixture with potato masher or beat with electric mixer on medium speed until creamy. Potatoes can be covered and refrigerated at this point up to 8 hours.
Sprinkle pecan mixture over tops of potatoes. Bake uncovered 30-35 minutes or until topping is brown and potatoes are hot.