Mushroom top is because the batter stuck near the mold wall and the batter in the center of the mold are heated differently. The thermal expansion coefficient is high or low. Because the surrounding surface adheres to the mold wall, a certain pulling force will be generated. So the increase around is not high, and the center is higher because it can expand freely without hindrance. It doesn't matter. You can flatten it if you don't like it. Cake shops are often so flat. Trim. I hope my answer can help you, and I hope it will be adopted. Thank you!