Mash the sweet potatoes until smooth using a potato masher. Add the whole milk or half-and-half, softened butter, granulated sugar, 1/4 cup light brown sugar, beaten eggs, vanilla extract, ground cinnamon, ground nutmeg, and kosher salt. Stir or mash together until everything is well combined and creamy.
Transfer the mashed sweet potato mixture to the prepared glass casserole dish, smoothing it into an even layer with a spatula. This is the base that will sit under the crunchy topping.
In a medium bowl, make the one crunchy mixture by combining 1/2 cup packed light brown sugar, all-purpose flour, chopped pecans, and melted butter. Stir with a fork until everything is evenly moistened and clumpy; it should look like a chunky, buttery crumble.
Hold the bowl of crunchy mixture over the glass casserole dish and use your hands to sprinkle the mixture evenly over the mashed sweet potatoes. Aim for good coverage so every scoop gets some of that brown sugar–pecan crunch. This is the moment that matches those close-up process shots—just you, your hands, and that glass casserole dish.
Place the casserole on the middle rack of the preheated oven and bake for 30–35 minutes, or until the topping is golden brown and crisp and the sweet potatoes are heated through and slightly puffed around the edges.
Remove from the oven and let the casserole rest for at least 10 minutes before serving. This helps the layers set a bit, making it easier to scoop clean portions with both creamy sweet potatoes and crunchy topping in every bite.
Variations & Tips
To make this ahead for a busy holiday or work week, prepare the mashed sweet potato layer and spread it in the glass casserole dish, then cover and refrigerate up to 2 days. Mix the crunchy topping ingredients just before baking and sprinkle over the chilled potatoes, adding 5–10 extra minutes to the bake time. For a slightly lighter version, swap the whole milk for evaporated milk or a splash of unsweetened almond milk and cut the sugar in the potato mixture in half. If you need it nut-free, skip the pecans and use rolled oats or crushed cornflakes in the topping instead, still mixing them with brown sugar, flour, and melted butter for texture. You can also play with warm spices—add a pinch of ginger or allspice, or increase the cinnamon for more of a dessert feel. For a smaller household, halve the recipe and bake it in an 8×8-inch glass dish, or bake the full batch and portion leftovers into individual containers; they reheat well in the microwave for quick weeknight sides. If you like a more rustic texture, only lightly mash the sweet potatoes so there are some small chunks left under the crunchy topping.
