Wash whole sweet potatoes thoroughly and poke on all sides with a fork to allow steam to escape while cooking.
Arrange yams in a spoke pattern on several layers of paper towel in the microwave.
Cook on the "baked potato" setting or until yams are soft all the way through when poked with a fork.
Remove from microwave oven and allow to sit and cool for 30 minutes or until they are cool enough to handle.
Slice yams in half lengthwise and scoop out cooked contents with a spoon. Discard skins.
In a bowl, combine yams, butter, maple syrup, vanilla extract, and ¼ cup of brown sugar. Mix well, mashing with a fork or potato masher until most lumps are smooth.
Spread yam mixture into a large pie plate or casserole dish.
To make the simple streusel, use a pastry blender to mix cold butter, baking mix, and brown sugar.
Chop pecans into small pieces and stir into streusel mixture.
Sprinkle crumble topping evenly over the top of the casserole.
Bake at 375 degrees for 20-25 minutes or until the streusel begins to brown. Remove from oven and serve immediately.