If your cake is undercooked in the middle but not on the sides, there are a few potential reasons for this issue:
Oven temperature: One possibility is that your oven temperature is not calibrated correctly. If your oven runs hotter on the sides or has hot spots, the edges of the cake may cook faster than the center. Use an oven thermometer to check the accuracy of your oven temperature and adjust accordingly.
Pan size and type: The size and type of the cake pan you use can affect how the cake bakes. If the pan is too deep or has a smaller diameter, it may take longer for the center of the cake to cook through. Consider using a shallower pan or adjusting the baking time and temperature accordingly.
Over-mixing: Over-mixing the batter can lead to a dense and undercooked center. When you mix the ingredients, be sure to mix just until the ingredients are incorporated. Over-mixing can develop gluten and result in a tougher texture.
Opening the oven door too early: Opening the oven door too early while the cake is still baking can cause a drop in temperature, which can affect the even cooking of the cake. Avoid opening the oven door until the cake is almost done to prevent heat loss.
Incorrect baking time: It's possible that the cake needs more time to bake. Check the doneness of the cake by inserting a toothpick or a cake tester into the center. If it comes out with wet batter or crumbs, the cake needs more baking time. Adjust the baking time accordingly and keep an eye on the cake to prevent over-baking.
Uneven distribution of batter: Make sure you evenly distribute the cake batter in the pan. If there's more batter towards the center or if it's not spread evenly, it can result in uneven baking.
By addressing these potential issues, you can improve the evenness of your cake's baking and ensure that the center cooks through properly.