5 sweet potatoes, peeled and sliced
1 1/2 cups butter
1/2 cup brown sugar
1 teaspoon ground nutmeg
3 tablespoons baking powder
2 teaspoons vanilla extract
1 1/2 cups packed light brown sugar
1 teaspoon lemon zest
1 (16 ounce) can sweetened condensed milk
Preheat oven to 375 degrees F (190 degrees C).
Grease and flour a 9x13 inch pan.
Place the sweet potatoes on a large baking sheet. Microwave them in 1/2-inch batches for 5 minutes. Cover and sprinkle with sugar, brown sugar and nutmeg. Bake uncovered for 15 minutes.
When cool, cut sweet potatoes into 1 inch cubes. Place them on the prepared baking sheet.
Meanwhile, combine the butter, brown sugar, nutmeg, baking powder and vanilla. Spread over the sweet potatoes, then spoon the brown sugar mixture over the tops of the sweet potatoes. Sprinkle lemon zest over the top of the casserole and spread evenly on the baking sheet.
Bake in preheated oven for 45 minutes. Remove from oven and sprinkle with brown sugar, lemon zest and condensed milk. Bake for another 15 minutes. Serve warm.