Preheat the oven to 350˚F.
In a large bowl, fold together the softened butter and the sweet potatoes with a spatula. Add the eggs, vanilla, sugar, and milk, and stir until well combined. Place the sweet potato mixture in a 9x9 glass casserole dish or deep pie pan. Alternatively use 2 shallow pie pan or it will overflow.
In another bowl, rub the butter into the brown sugar, and flour until it clumps together when pressed in your hand. Add in the pecan and mix to combine.
Cover the sweet potato mixture with the pecan crumble and place in the preheated oven for 30-35 minutes. Bake until the mixture has fluffed and the crumble is caramelized.
Allow to cool about 10 minutes and serve directly from the pan.