Preheat oven to 350° Fahrenheit. Adjust oven racks as needed so pan can sit in center of oven. Set up wire cooling racks over thick layer of paper towels and set aside. Place pecans in large mixing bowl and set aside. For easier cleanup, line large baking sheet with parchment paper. Set aside.
Place butter in small bowl and place bowl in microwave. Microwave butter in 15-20 second increments, stirring between each, until butter is fully melted. Be careful not to burn or boil butter.
Pour melted butter over pecans in large bowl. Toss or stir until pecans are well-coated. If desired, add salt now and toss until pecans are coated in salt and butter. Alternately, wait to add salt until after toasting.
Transfer buttered pecans to baking sheet. Spread pecans out in one even layer, making sure nuts don't touch or overlap if possible. Place baking sheet in preheated oven.
Toast pecans 5 to 10 minutes, then carefully remove baking sheet from oven. Use silicone spatula or wooden spoon to stir and turn pecans over, then return baking sheet to oven. Repeat process of toasting then stirring every 5 to 10 minutes, cooking up to 30 minutes total as needed. Note: check doneness each time pecans are stirred. Stop cooking once nuts are fully toasted and rich brown in color, but not burned. Be careful not to overcook or burn pecans.
When desired doneness is achieved, remove baking sheet from oven. If salt was not added before toasting, sprinkle salt over hot pecans immediately.
Transfer toasted pecans to wire cooling rack. Let pecans cool, then serve warm or at room temperature. Alternately, transfer room temperature pecans to airtight container until ready to serve.