Preheat the oven to 350 degrees.
Grease a 2.5 quart casserole dish.
Peel and chop the sweet potatoes into chunks.
Place in a stockpot with enough water to nearly cover.
Bring to a boil over medium-high heat. Reduce heat and simmer for 20 minutes, until sweet potato chunks are tender enough for mashing.
While the sweet potatoes are cooking, mix the topping ingredients together. Melt the butter in a mixing bowl in the microwave for about 30 seconds, then add the flour and brown sugar. Stir until combined.
Drain and mash the sweet potatoes.
Mix in the sugar, eggs, butter, and vanilla.
Pour the sweet potato mixture into the casserole dish.
Spread the topping over the sweet potato mixture.
Bake in the oven for 30 minutes.