Preheat the oven to 350°F. Line a 9-inch pie dish with a prepared pastry crust.
Take the lemon, trim the pointy edges off, then slice it and take the seeds out. Put the lemon slices into the blender.
Add the eggs, sugar, and melted butter to the blender. Blend on high until it is all smooth and no chunks of lemon rind are left behind.
Pour the lemon filling into the prepared, unbaked pie shell.
Bake at 350°F for 45 minutes.
Remove from oven and let cool to room temperature. Either dig in right away or refrigerate for a couple of hours first. Refrigerate any leftovers, covered so it doesn’t dry out.