Cut the top off of the pumpkin, ensuring that you’ll have adequate access to to scoop the seeds from both halves. Alternatively, if the pumpkin is too large, just cut it in half instead.
Scoop out the seeds and pulp with a large spoon, transferring everything to a bowl.
Submerge the seeds and pulp in a bowl of water. Skim the floating seeds off the top to separate them from the pulp and strings. Use your hands to help separate the seeds from the pulp.
Rinse the seeds thoroughly in a colander. Discard the pulp.
Bring 4 cups water and 1 tablespoon kosher salt to a boil in a saucepan.
Transfer the seeds to the saucepan and boil for 10 minutes.
Drain the seeds well and spread them in a single layer on a clean kitchen towel or paper towels. Let them air dry for at least 1 hour, or leave uncovered overnight for the driest, crispiest result.
Preheat the oven to 300 F.
Line a baking sheet with parchment paper.
Toss about 2 cups of dried seeds with the melted butter, maple syrup, smoked paprika, cayenne, cumin, and remaining 1 tablespoon kosher salt.
Spread the seeds in a single layer on the prepared baking sheet. Roast for 25 minutes, stirring every 8 minutes, until deep golden brown and crisp.
Remove from the oven and sprinkle immediately with flaky sea salt. Let the seeds cool completely on the baking sheet to crisp up even more before serving.