If you want to skip the cooking process, there are a few ways to effectively "buy" a cake:
Birthday cake rant. Am I missing an easy option or? : r/Sims4 sims 4 buy birthday cake
: If you have the Dine Out game pack, you can visit any restaurant, click on your table, and order a cake to be delivered immediately. You can then place candles on it right at the restaurant or drag it into your Sim's inventory to take home. If you want to skip the cooking process,