Preheat your oven to 180°C (350°F) and lightly grease a medium baking dish.
Place the peeled and chopped sweet potatoes into a large pot, then cover with salted water.
Bring the water to a boil over medium-high heat, then simmer until the sweet potatoes are tender and easily pierced with a fork, about 15 minutes.
Drain the sweet potatoes thoroughly and transfer them to a mixing bowl.
Use a masher or fork to mash the sweet potatoes until smooth and creamy, then stir in melted butter, a splash of milk, and a pinch of salt until well combined.
Spread the mashed sweet potatoes evenly into the prepared baking dish, smoothing the surface with the back of a spoon.
In a small bowl, mix the crushed pecans, brown sugar, and cinnamon to make the topping mixture.
Sprinkle the pecan topping evenly over the sweet potato layer.
Bake the casserole in the oven for 25 to 30 minutes, until the topping is golden brown and the casserole is bubbling around the edges.
Remove from the oven and let it rest for 5 minutes to settle before serving.
Serve warm, enjoying the contrast of soft sweet potatoes and crunchy pecan topping with a warm cinnamon aroma.