Prepare the Cake: Preheat the oven to 350°F and grease a 13×9-inch baking pan.
Mix Wet Ingredients: In a large mixing bowl, blend sweet potatoes and milk until smooth. Stir in eggs and vanilla.
Combine Dry Ingredients: In a separate bowl, whisk together flour, sugar, salt, baking powder, and nutmeg.
Combine and Bake: Gradually mix dry ingredients into the sweet potato mixture until just combined. Gently fold in melted butter. Pour batter into the prepared pan and smooth the top.
Create the Swirl: Mix softened butter, brown sugar, cinnamon, and flour in a bowl. Drop spoonfuls over the batter and swirl with a knife.
Bake to Perfection: Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean. Let cool for 20 minutes.
Drizzle the Glaze: In a bowl, whisk powdered sugar, milk, vanilla, and chopped pecans until smooth. Drizzle over the slightly warm cake and let it set before slicing.