Place the thinly sliced onions in a glass jar.

In a small saucepan, simmer the vinegar, sugar, salt, and pepper, until sugar and salt dissolves.

Pour hot vinegar mixture over onions and let stand until cool. Refrigerate for 2 days and up to 2 weeks.

To make perfect hard-boiled eggs: place eggs in a saucepan, cover with cold water, and place over high heat. Once eggs come up to a boil, turn off the heat and cover for 11 minutes.

Crack shells and cool in ice water. Peel, cut in half, and remove yolks.

Place yolks in a small bowl and mash with mayonnaise, mustard, and salt & pepper.

Pipe mixture back into egg whites, top with pickled onions and a sprinkling of sweet paprika.