Heat oven to 350 degrees. Generously butter a 10-inch deep dish pie plate or springform pan.
Spread cranberries over the bottom of pie pan (no need to thaw if frozen), sprinkle with nuts if using and then pour the maple syrup evenly over all.
Beat the eggs in a large bowl, preferably with a spout for pouring. Add brown sugar and beat until no lumps remain.
Add the flour, baking powder, and melted butter - beat well. Pour the batter evenly over the top of the cranberries.
Bake at 350 for 35-40 minutes, or until top is browned. Remove from oven and let cool
While cooling, make optional glaze by whisking the powdered sugar and milk together in a small bowl until pourable consistency (start with 1 tablespoon milk and add more only if needed).
Serve the pie either warm or cold for dessert, brunch or with tea and coffee.
Notes
Orange-Cranberry Pie Variation:
Sprinkle zest of 1 large orange over the cranberry layer.
Use orange juice instead of milk to make the glaze.
Storage:
Store covered at room temperature for 1-2 days. Refrigerate pieces in a covered container, or cover the whole pie well, for 3-4 days.
Freeze the whole pie up to 3 months - cover the top with plastic or waxed paper and then the whole plate with foil. Label and freeze. Freeze individual pieces by wrapping in foil or placing in freezer containers for 3 months. Thaw overnight before serving.
Serve this warm or cold. To reheat, microwave pieces for 20-30 seconds or heat in an air fryer/toaster oven for a minute or two.