Bring butter to room temperature.

Heat water in a microwave-safe container for 40 seconds at 600W.

Mix bread flour, sugar, salt, dry yeast, butter, beaten egg, and warm water in a bowl until combined. Knead on a surface for 10–15 minutes until smooth.

Place the dough back into the bowl, cover loosely with plastic wrap, and let it rise at 40°C for 30 minutes using the oven's proofing function.

Prepare the filling: Trim the root of the shimeji mushrooms and separate them. Cut bacon into 5mm slices.

Heat olive oil in a pan over medium heat. Cook bacon until browned, then add mushrooms and sauté until softened. Season with salt and pepper. Let cool.

Punch down the dough gently to release gas. Divide into 6 portions and shape into balls. Place each ball in an aluminum cup and press the center thin while keeping the edges thick.

Cover loosely with plastic wrap and proof again at 40°C for 20 minutes.

Add the filling to the center of each dough ball. Brush with beaten egg and sprinkle shredded cheese on top.