Thaw the puff pastry: Leave the puff pastry sheet at room temperature until fully thawed, about 30 minutes (or thaw overnight in the fridge).
Preheat the oven to 400°F (200°C). Place a muffin tin on a baking sheet to catch any drips, then grease the muffin cups well with cooking spray (or butter).
On a lightly floured surface, roll out the thawed puff pastry just enough to smooth it. Cut into 6 squares large enough to line the muffin cups with a little overhang.
Press one pastry square into each muffin cup, gently shaping it into a cup.
Place 1 slice ham into each pastry cup, pressing it against the sides.
Crack each egg into a small bowl first (to avoid shells), then carefully pour 1 egg into each ham-lined cup.
Sprinkle cheddar evenly over the eggs. Season with salt and pepper. (Optional: lightly brush exposed pastry edges with melted butter for extra browning.)
Bake for 18–22 minutes, until the pastry is golden and the egg whites are set. For runnier yolks, start checking closer to 18 minutes.
Cool in the tin for 2–3 minutes, then use a spoon or butter knife to gently lift each cup out. Transfer to a cooling rack.
Top with microgreens just before serving. Enjoy warm while the cheese is melty and the pastry is crisp.