Start by cooking your sweet potatoes. You can bake or boil. (Baking is easier; boiling is faster.)

To bake: I like the baking method best, I think it's easiest! Preheat your oven to 400 degrees F. Poke each sweet potato firmly with a fork, two pokes on each side. Place on a pan lined with tin foil. Pop them in the oven and roast at 400 for 45-60 minutes until completely tender. You should be able to stick a butter knife all the way through with very little resistance. The thicker your sweet potatoes, the longer it will take.

To boil: Peel the sweet potatoes and chop into 1 or 2 inch pieces. Add to a large pot filled with water. Bring to a boil over high heat, then turn down to a simmer. Let simmer for 25-30 minutes until fork tender. Drain very well using a colander.

Make the sweet potato filling: In a large bowl, add sweet potatoes. You should have about 5 cups. Add 5 tablespoons butter, 1/2 cup milk, 3/4 cup packed brown sugar, 1 and 1/2 teaspoons kosher salt (add 1 and 1/4 teaspoon if using table salt), 1 teaspoon vanilla, 1 tablespoon fresh lemon juice, and 2 large eggs.

Mash it all together with a potato masher. If you like REALLY fluffy sweet potato casserole with zero lumps, use a hand mixer to beat it together for a couple minutes. (I prefer mine thoroughly mashed with a potato masher.)

Spread the sweet potato mixture evenly into a 9x13 inch pan, smoothing out the top. (At this point you can refrigerate it ahead of time and bake up to two days later. See notes!)

Preheat your oven to 350 degrees F.

Make the streusel. In a medium bowl, add 1 and 1/2 cups flour (spooned and leveled), 1/2 cup packed brown sugar, 1/4 cup sugar, 1/2 teaspoon kosher salt, 1 tablespoon cinnamon, 1/2 teaspoon nutmeg, 1/4 teaspoon cardamom, and 1 cup chopped pecans. Whisk it all together.

In a large bowl, melt 1/2 cup (1 stick) butter. Pour the dry streusel ingredients into the large bowl with the butter (then wipe out the medium bowl and stick it back in the cupboard.)

Use a spatula to mix together the streusel. Make sure all the dry ingredients are moistened with butter.

Use your fist to pick up handfuls of streusel. Squeeze it together and gently crumble it over the top of the sweet potatoes so that they stay in big chunks.

Bake. Bake at 350 for 25-30 minutes, until the streusel looks dry and crumbly and slightly browned. Halfway through the bake time, at about the 15 or 20 minute mark, I like to sprinkle on an extra 1/3 cup chopped pecans. (If you add them in the beginning they will burn.) This is optional but I love the extra crunch and how pretty it is.

Serve warm! See notes for how to make this ahead of time. You can make this earlier in the day on Thanksgiving. Bake it as directed, and then set it aside somewhere on the counter in your mess of a kitchen. (Don't refrigerate, or even bother covering) Then you can reheat it right before serving. About 15-20 minutes in a 350 degree oven will be enough to get it warmed through!

Store leftovers covered in the fridge. It will keep for 3-5 days!