Mix the mayonnaise, Dijon mustard, lemon juice, and black pepper in a small bowl. Set aside. Keep this layer thin. The sauce should season the sandwich, not soak the croissant. Keeping that layer genuinely thin protects the croissant's own delicate, flaky structure from absorbing excess moisture before the sandwich is even fully assembled.

Place the bacon in a cold skillet and set it over medium heat. Cook until crisp and deeply golden, about 8 to 10 minutes, turning as needed. Transfer to a paper towel-lined plate. Crispy bacon matters here because the croissant and eggs are soft. If the bacon is limp, the whole sandwich eats heavy. Starting the bacon cold, rather than dropping it into an already-hot pan, gives the fat genuine time to render out gradually as the pan heats alongside it — bacon added directly to hot fat tends to seize and brown unevenly before its interior fat has fully rendered.

Split the croissants in half horizontally. Toast them cut side down in a dry skillet or warm oven for 2 to 4 minutes, just until the cut sides are lightly crisp and the edges feel flaky. The croissant should stay buttery and tender inside, but the cut side needs enough structure to hold the eggs and sauce. That brief, targeted toast builds real resistance specifically at the cut surface, which is exactly where the filling and sauce will sit, without pushing the rest of the croissant's naturally soft, layered interior toward dryness.

Whisk the eggs, milk or cream, salt, and black pepper in a bowl until smooth. Melt the butter in a nonstick skillet over medium-low heat. Add the eggs and cook slowly, stirring with a spatula, until softly set and still slightly glossy, about 3 to 5 minutes. Remove from the heat immediately. Stop before the eggs look dry. They should be soft and custardy because they will continue setting slightly inside the warm sandwich. Cooking over genuinely low heat with slow, gentle stirring is what produces large, soft curds capable of surviving that additional residual cooking without turning dry.

Place the cheese slices over the warm scrambled eggs for 30 to 60 seconds, just until softened and starting to melt. You can also place cheese directly on the bottom croissant halves and let the hot eggs melt it during assembly. Do not put the filled croissants under high heat for too long. Croissants burn fast and eggs overcook fast. Relying on the eggs' own residual warmth to melt the cheese, rather than any further direct heat, is what protects both the delicate croissant and the already-properly-cooked eggs from overcooking at this late stage.

Spread a thin layer of Dijon mayo on the top and bottom cut sides of each croissant. Add the cheesy scrambled eggs to the bottom halves. Top with crispy bacon, extra black pepper, and chives if using. Close with the top croissant halves. Spreading the mayo on both cut sides, rather than just one, gives the sandwich balanced flavour throughout while also lightly protecting both surfaces from the fillings' own moisture.

If using hot honey, warm the honey slightly and stir in chili flakes or hot sauce. Drizzle a very small amount inside the sandwich or over the bacon before closing. Warming the honey only slightly, rather than heating it hard, is enough to loosen it for drizzling while keeping the addition genuinely small and controlled against the sandwich's own richness.

Cut the sandwiches in half and serve immediately while the croissants are flaky, the eggs are soft, and the cheese is melted. This sandwich's whole appeal depends on catching every component — crisp cut edges, soft eggs, melted cheese, crackling bacon — together at their individual best, which is exactly why serving without delay matters.