This game is really adorable and fun! The aesthetic and the music is really lovely and the gameplay loop is very absorbing. I think this could definitely be made a longer and more complex game.
I would recommend that the steering wheel be lit up, at least in the beginning, when you have to control the temperature of the water. When I first played I was quite confused because, standing next to the tub, sometimes the instructions would appear and I could press 'E' but sometimes they didn't work. It took me a while to figure out that you had to stand directly next to the steering wheel. I also think there should be a way to change the temperature of the water if you make a mistake since apart from resetting the game you can't do anything about it, and that you should be able to add ingredients out of order.
I know that the instructions are written on the start screen when the game begins, but I also feel that the bell should be lit up when the player has finished preparing the bath to tell them to ring it. I feel that a lot of players are more likely to jump in and ignore the instructions on the title screen, haha. So maybe a tutorial level would be a good idea, especially if you don't want the game to constantly be lighting up parts like the steering wheel or the bell. Direct the player to set the temperature of the water, highlighting the steering wheel, then tell them to get the chocolate, then the milk, and finally the toppings, before ringing the bell. After that, the actual game can start with the player knowing what to do.
I would love to see the game fleshed out more and more levels added! Maybe you could add more types of milk, chocolate or toppings. Thanks for reading my long response, and for making this game!