To make Chef John's sweet potato gnocchi recipe, you'll first need to prepare the sweet potatoes. Peel and cut the Sweet Potatoes into small cubes. In a large bowl, mix together the flour, baking powder, salt, and nutmeg. Add the butter and mix until the mixture is light and fluffy. Stir in the beaten egg yolks and vanilla. Pour the dough into the prepared baking dish. Cover the dish with plastic wrap and refrigerate until firm, at least 1 hour. Bake at 450?F (230?C) for 20 to 25 minutes or until golden brown. Remove from the oven and allow to cool before serving.