Begin by preparing the bread bowls. Slice off the upper ¼ of the bread bowl, and use a knife to cut around the inside to hollow out the other ¾ of the bread. Set aside the hollow bread bowl and sliced off top onto a baking sheet for now, and cut the bread we removed into cubes. Lightly coat the bread cubes with oil and toast until it starts to turn golden brown. I did this in an airfryer at 200°C/400°F for 6 minutes, but you can also do this in an oven or toaster. Once toasted, set aside.

Next, prepare the bechamel sauce. In a saucepan, melt butter over medium high heat. Once the butter has melted, add the cake flour and whisk to create the roux. Mix around vigorously to ensure that the flour is evenly distributed and cooks evenly. Keep mixing around until the flour is completely cooked and turns a golden brown.

Add the milk in increments, stirring after each pour to prevent lumps. It may look like it won’t come together, but just keep adding and whisking.

Once the sauce is smooth and thick, add the heavy cream, bouillon powder, salt, and pepper to taste. Mix to fully incorporate and set aside.

Prepare the vegetables. If you are using different ingredients or omitting them, then you can skip this step! Heat up olive oil in a small pan over medium heat. Add the minced garlic and lightly fry until fragrant. Add the shimeji and onions and cook until the onions are translucent. Remove from the pan and set aside for now.

Using the same pan, heat up a little more oil to cook the spinach. Season the spinach with a pinch of salt, and cook until wilted then remove as well.

Now we can mix the ingredients all together. In a bowl, add the toasted bread, bechamel sauce, and any vegetables or protein you are using. Fold together and scoop the mixture into the bread bowls. It’s okay if the filling goes a little bit higher than the top of the bread.

Top with mozzarella cheese and bake with the sliced off tops at 180°C/350°F for 10-15 minutes. If the tops start to get too brown, remove from the tray and continue baking the bowls. Additionally, if the bowls are toasting faster than the cheese is melting, you can use a broiler on low to melt the cheese on top.

Once the bread is golden and the cheese is melty and bubbly, remove it from the oven. The filling will be really hot, so be careful! Plate the bread gratin to serve immediately, and the bread gratin is done! 完成です！