1 cup farro, spelt, or wheat berries
2 cups finely grated Parmesan, divided
1 cup heavy cream
1 cup whole milk
2 teaspoons kosher salt
Pinch of nutmeg
4 large eggs
special equipment: An 8-inch-diameter springform pan with a tight seal
Preheat oven to 350°. Generously grease pan with oil. Wrap outside of pan tightly with foil (this will help prevent custard from leaking out). Line a rimmed baking sheet with parchment or foil. Place springform pan on sheet.
Place farro on another rimmed baking sheet; toast in oven until fragrant and slightly darker in color, about 15 minutes.
Meanwhile, bring a large saucepan of salted water to a boil.
Add toasted farro to boiling water and cook until tender but still al dente, 20–25 minutes. Drain; let cool slightly.
Whisk 1 3/4 cups Parmesan, cream, milk, salt, nutmeg, and eggs in a large bowl. Fold in cooked farro. Pour mixture into prepared cake pan and bake until puffed and just set in center (center will jiggle slightly when pan is nudged), about 40 minutes. Remove from oven. Preheat broiler.
Sprinkle remaining 1/4 cup Parmesan over top of pie. Broil until top is golden brown, 3–4 minutes.
Let cool for 30 minutes. Run a sharp paring knife around edge of pan to loosen pie; remove pan sides.
Cut pie into wedges. Serve warm or at room temperature.