1. HOLLANDAISE SAUCE: Combine vinegar, juice and peppercorns in small saucepan; bring to the boil. Reduce heat; simmer, uncovered, until liquid is reduced by half. Strain through a fine sieve into small heatproof bowl; cool 10 minutes.
2. Whisk egg yolks into vinegar mixture. Set bowl over small saucepan of simmering water; do not allow water to touch base of bowl. Whisk mixture over heat until thickened. Remove bowl from heat; gradually whisk in melted butter in a thin steady stream, whisking constantly until sauce is thick and creamy.
3. POACH EGGS: To poach eggs, half-fill a large shallow frying pan with water; bring to the boil. Break 1 egg into a cup, then slide into pan; repeat with three more eggs.
4. When all eggs are in pan, allow water to return to the boil. Cover pan, turn off heat; stand about 4 minutes or until a light film of egg white sets over yolks. Remove the egg with a slotted spoon and drain on absorbent paper; cover to keep warm. Repeat with remaining eggs.
5. Meanwhile, split muffins in half and toast. Serve muffins topped with ham, poached eggs, sauce and chives.