Cook bacon strips in a large skillet over medium heat for 6-8 minutes until crispy, flipping halfway. Drain on paper towels, chop into bite-sized pieces, and set aside. Pour off all but 1 tablespoon of grease from the skillet.

Whisk eggs with milk, salt, and pepper in a bowl. Pour into the skillet with reserved bacon grease and scramble over medium-low heat, stirring gently until just set but still slightly soft. Remove from heat immediately.

Lay a flour tortilla flat. On one half, layer ¼ cup cheese, scrambled eggs, bacon pieces, and another ¼ cup cheese. Fold the empty half over to create a half-moon shape. Repeat with remaining tortillas.

Heat a clean skillet over medium heat with a pat of butter. Place one quesadilla in the skillet and cook for 2-3 minutes per side, pressing gently with a spatula, until golden brown and crispy with melted cheese inside.

Remove to a cutting board, let rest 1 minute, then cut into wedges. Serve hot with salsa and sour cream if desired. Repeat with remaining quesadillas.