Preheat the oven to 400°F (205°C).
Unroll a premade pie crust over the bottom of a 9.5-inch pie plate or deep dish pie pan.
Trim the edges, leaving a half-inch overhang. Fold the overhang over, lightly press it against the rim of the pie plate, and use a fork or your fingers to crimp it decoratively.
In a medium bowl, whisk the butter and sugar together until light and fluffy. Add the eggs and vanilla. Continue mixing.
Next, stir in the flour, lemon zest, nutmeg, and salt. Continue beating until smooth.
Finally, add the buttermilk, followed by the pineapple chunks, if desired, and mix.
Pour the buttermilk filling into the prepared crust and bake at 400°F (205℃) for 10 minutes. Then reduce the heat to 350°F (180℃), and bake it for 50-60 minutes.
Remove the pie from the oven and let it cool for an hour or more before serving. If adding pineapple, you might have to let it cool longer.
Serve at room temperature with whipped cream.