Add the egg, sugar, condensed milk, and melted butter into a bowl, mixing with each addition.
Sift in the cake flour and baking soda, and mix with a rubber spatula.
Once the dough comes together, wrap in plastic wrap, and let rest in the fridge for about 30 minutes.
In the meantime, divide the anko into 9 portions and roll up into balls.
Divide the rested dough into 9 pieces, roll them out (with your hands is fine), wrap up the anko, and place them on a baking sheet lined with parchment paper. Make sure place them seam side down.
Brush the surface with the leftover egg using the back of a spoon or a brush, and bake for 10 to 15 minutes in a preheated 180℃ oven. (Adjust the time accordingly.)
It's done. Once cooled, wrap in plastic wrap and they will become even moist with time.
I used chunky anko this time, but you can also use a finely mashed anko, or put a chestnut inside!
Story Behind this Recipe
I don't have a steamer, so I just made this easy-to-make baked manju in the oven. It's homemade, and only costs about 20 yen each. 1 manju = about 90 kcal.
When I say "leftover egg" at Step 6, I mean the other half of the medium sized egg, since we're only using one half for the batter. The butter can be salted or unsalted. I wanted to add some richness and moistness, which is why I used condensed milk, but you can just make this with sugar (about 40 g in that case) as well.