Butter-filled and deep-fried.
Here’s a baked version (yikes) from the April 1, 1870 edition of the Rochester (Indiana) Union Spy:
Stuffed Eggs. — Halve ten hard-boiled eggs lengthwise; take out the yolks, pound them in a mortar; add to them some bread crumbs soaked in milk, and a quarter of a pound of fresh butter; pound all together; add a little chopped onion and parsley, some bruised pepper, and grated nutmeg; mix it with the yolks of two raw eggs; fill the halved whites with some of this forcemeat; lay the remainder at the bottom of a dish, and arrange the stuffed eggs upon it; put into an oven, and when nicely browned, serve.
From the box of A.D. from Lutz, Florida, by way of Pennsylvania in the 1940s, and originating in Ohio in the 1920s.
6 eggs (to hard-boil)
1 egg (for filling)
2 Tbsp. butter
1 tsp. cream
2 or 3 drops onion juice
Hard boil the eggs and cut them in half. Remove yolks and mash fine. Add 2 Tbsp. butter, 1 tsp. cream, 2 or 3 drops of onion juice and salt and pepper to taste. Mix well. Fill eggs and place halves together. To the filling left, add a well-beaten egg. Cover eggs with this and roll in cracker crumbs and fry in boiling lard till a light brown.
This recipe calls for 6 eggs.