1. Preheat oven to 350°F Convection Mode with a rack set at position “3.” Melt 1 tablespoon of butter with olive oil in a large heavy skillet over medium heat.
2. Add scallions and cook until soft, about 3 minutes.
3. Remove pan from heat and pour scallions into a small work bowl.
4. Add spinach, feta, dill, nutmeg, and pepper, stirring to combine.
5. Melt remaining 4 tablespoons of butter in a small saucepan.
6. Remove the thawed phyllo from the package and unroll, leaving all the sheets still in a single stack.
7. Cut the phyllo stack with a pizza cutter into 3 long strips.
8. Cover the phyllo with a towel to prevent it from drying out.
9. Peel the layers apart and lay 4 strips down on the counter.
10. Brush with melted butter and top with another layer of phyllo. Brush this layer also.
11. Place a small amount of filling in the corner nearest you and fold the phyllo over onto itself, making right triangles along its length (like folding a flag). Repeat with remaining strips of phyllo.
12. Brush the folded triangles with melted butter.
13. Place spanakopita on a baking sheet lined with parchment paper. Bake until golden brown about 15–18 minutes.