Preheat oven to 400 degrees F. Slice squash in half lengthwise and remove seeds and stringy insides. Place squash cut side facing up on a rimmed baking sheet. Inside each squash half, place 1/2 tablespoon of butter and 1 tablespoon of maple syrup. Sprinkle all of the squash with sea salt (about 1/2 teaspoon total). Roast for 40 minutes or until tender.

Let cool, then spoon out the squash (including the butter and maple syrup) into a bowl. Place squash in blender with orange juice and zest, eggs, 2 tablespoons melted butter, baking powder, and 2 tablespoons of maple syrup. Then stir in 1 teaspoon vanilla, and the other half teaspoon of salt.

Transfer the squash mixture to a greased 3-quart casserole dish. (At this point, the casserole can be covered and refrigerated overnight.)

In a large saucepan over medium heat, combine pecans, brown sugar, the remaining 2 tablespoons of maple syrup, 1/8 teaspoon salt, the remaining butter (3 tablespoons) and 1 teaspoon vanilla and bring to a boil. Cook for 2 minutes more, then pour over squash mixture. Bake until bubbly, about 45 minutes.