Combine everything for the meat mixture in a bowl: ground beef, onion, flour. Add the panko, milk, and mix.
For Christmas, I used colorful vegetables. Usually I use shiitake mushrooms, cheese, etc.
Mix very well. Make into a large clump. Toss it around in the bowl to get rid of any air. Do this several times.
Spread parchment paper into a rectangular baking pan. Pour in your mixture, making sure to stuff it in well. Leave the top of the sheet open. Bake in a pre-heated oven for 10 minutes at 230°C or 20 minutes at 180°C.
Once it's finished, let it sit for awhile. Use the ◎ juices from baking for the sauce.
The sauce: the cooking juices are difficult to mix in, so be sure to mix verrrrry well.
This is a version with shiitake and cheese.
Story Behind this Recipe
Just leave it to your oven.
Use the cooking juices in the sauce.. As for the difference in cooking temperatures. At 230 ℃, the top layer gets a nice baked color. At 180 ℃ ,the bottom layer bakes thoroughly.