Fill a large pot half full with water and bring to a boil. Add salt and Old Bay and return to boiling.
While the water comes to a boil, place butter in a small saucepan to melt over medium-low heat. Once the butter starts to foam, after about 1 minute, remove from heat and let stand for 5 minutes while the crab cooks. Use a spoon to remove the milk solids floating on top of the butter. Pour clarified butter into a small bowl.
Add crab legs to pot of boiling water and reduce heat to medium. Simmer for 5 to 6 minutes until fragrant.
Remove crab from the pot and serve immediately. I sprinkle a little more Old Bay over the crab and serve it with lemon wedges and melted butter.
Notes
If you're making a lot of crab legs, you can work in batches and keep using the same water to boil the rest of your crab.