Cajun Hollandaise Sauce: In small saucepan, heat butter over medium‐high heat until melted and bubbling. In blender, purée egg yolks, lemon juice and mustard until smooth. With motor running, pour the bubbling butter into blender in thin stream. (Add 1 to 2 tbsp/15 to 30 mL water if sauce is too thick.) Season with Cajun seasoning; keep warm.
Meanwhile, fill saucepan with enough water to come 3 inches (8 cm) up side; heat to gentle simmer. Stir in vinegar. Break cold egg into small dish or saucer. Holding dish just above simmering water, gently slip egg into water. Repeat for remaining eggs. Cook in barely simmering water until white is set and yolk is cooked as desired, approximately 3 to 5 minutes. Remove eggs with slotted spoon. Drain well on paper towel.
Top each slice of corn bread with crumbled sausage and poached egg. Spoon Cajun Hollandaise Sauce over top. Garnish with green onion.