Cook bacon strips in a large skillet over medium heat until crispy, about 8-10 minutes, turning occasionally. Drain on paper towels. If using Canadian bacon or ham, warm in the skillet for 1-2 minutes per side.

Whisk eggs with milk, salt, and pepper in a bowl until well combined.

Melt butter in a non-stick skillet over medium-low heat. Pour in the egg mixture.

Cook gently, stirring slowly with a spatula, until eggs are just set but still slightly glossy — about 3-4 minutes. Remove from heat while still slightly underdone as they will continue cooking from residual heat. Season with salt and pepper.

Lightly toast the croissants cut-side down in a dry skillet or under the broiler for 1-2 minutes until golden.

Place a slice of cheese on the bottom half of each croissant while it is still warm so the cheese melts slightly.

Top with a generous portion of scrambled eggs, then 2 strips of crispy bacon. Add any optional toppings. Close with the top half of the croissant and serve immediately.