Preheat oven to 400°F then bake sweet potatoes on a parchment lined sheet tray for about 90 minutes. When sweet potatoes are soft and oozing brown out the sides they are done. Set aside and let cool slightly
Making Brown Butter
Cook butter in a medium sauce pot over low-medium heat until melted. Add sage leaves. Let butter sputter, giving an occasional stir. Butter will slowly stop bubbling and become quiet, it will be a medium brown color. Remove from heat immediately and set aside. Remove sage leaves before blending with sweet potato
Mixing Sweet Potatoes
Blend sweet potatoes in a large mixing bowl on medium speed until smooth
Mix in salt, brown butter, brown sugar and evaporated milk
Transfer mixture to pie pan or baking dish, top with marshmallows then bake for 5-7 minutes until marshmallows are puffed and brown
Notes
Make this dish up to 3 days ahead of time. Leave the marshmallows off until you are ready to serve. I actually think this sweet potato pudding recipe taste better the second day.
If you make this with the marshmallows, you can still keep it and reheat it. I suggest covering the whipped sweet potatoes with plastic wrap then microwaving until warm.
Fresh sweet potatoes are best for this recipe. That way you're able to roast them and let the insides start to caramelize.
I use Diamond Crystal kosher salt. Using kosher salt comparted to iodized table salt when cooking and baking makes a huge difference. If you're using Morton's kosher salt then use 75% of what's called for in the recipe.
Watch your brown butter closely and remove it from the heat as soon as it's ready. Read the section below on how to make brown butter.
If you want to make sure your sweet potatoes are extra smooth then you can use a food processor. I find that an electric hand mixer works well but may leave a few strings.