Place a medium skillet over medium heat and add 1 tsp oil or a small pat of butter if using. Once warm, lay 2 bacon slices in a single layer. Cook 3–5 minutes per side until crisped to your liking, adjusting heat so it does not burn. Transfer cooked bacon to a paper-towel-lined plate to drain. Reserve 1 tsp of bacon fat in the skillet for flavor (optional) or wipe skillet clean if you prefer no fat.

Eggs

Beat egg

In a small bowl, crack 1 large egg and add 1 tablespoon milk, 1 teaspoon salt, and 1/4 teaspoon freshly ground black pepper. Whisk until uniform and slightly frothy.

Cook egg

Heat the same skillet over low–medium heat (use reserved bacon fat or add 1 tsp butter). Pour the beaten egg into the skillet. For a folded/sandwich-style egg: let edges set (~30 seconds), then gently push cooked edges toward the center while tilting the pan so uncooked egg flows out, repeating until mostly set but still tender, about 1–1½ minutes total. For a fried egg alternative: crack the egg into the pan and cook to desired doneness. Remove the egg when just set; it will continue to cook slightly while assembling.

Croissant & Assembly

Prep croissant

If the croissant is cold, warm it in a 350°F (175°C) oven for 3–4 minutes or toast gently cut-side down in a dry skillet for 1–2 minutes until lightly crisp and warmed through. Cut the croissant in half lengthwise.

Butter and cheese (optional)

Spread 1 teaspoon softened butter on the cut sides of the warm croissant. If using cheese, place the slice on the bottom half of the croissant immediately after removing the egg so the residual heat melts it slightly.

Assemble sandwich

Layer the ingredients: bottom croissant half, cheese (if using), warm egg, 2 bacon slices (broken to fit if needed), spinach leaves and tomato slices (if using), a light drizzle of hot sauce or a smear of Dijon mustard (if using), then top croissant half. Press gently to compact.

Finish

Cut the sandwich in half if desired and serve immediately while warm.