If you notice your cake is forming cracks on the top, that means your oven is too hot or the cake was placed too high in the oven. The crack is caused because the crust is formed much earlier due to the hot oven while the cake continues to rise. This does not alter the taste, but if it happens in the first 15 minutes, then reduce the temperature or move the cake to the lower rack and continue to bake. At least you will save it from having more cracks which you can always hide with toppings, frosting or icing!