is this a good way to stop sponge cake cracking when cooking? covering with baking paper...?!
The way bakers usually say to not let cakes cracking is to put a pan in the bottom rack with water. I just saw a sourdough bread recipe that said to spray the oven several times throughout the baking period as well.
I would do it without the baking parchment. If it does crack, don't worry it will look more authentic and home-made.
If you want to check whether your cake is cooked inside just stick a skewer in the middle and if it comes out clean its cooked, another way to tell (if you can't find a skewer or can't be bothered to find one) is ,once you've taken it out of the oven, to poke the cake lightly and if the cake springs back it is done.
If it will be covered in buttercream, I don't see why it matters. But yes, you can probably stick parchment paper on top and then peel it off as the baked cake cools. Fold up one corner so you have a place to grab and pull.
You just answered your own question.
maybe. have a try.