Learn Portuguese (Portugal): O sabor deste bolo é ótimo.

In Portuguese, the preposition de (of) always merges with the word este (this) to form the contraction deste. Because bolo is a masculine word, we use the masculine form deste.

Why do we use é here instead of está?

Even though you are eating the cake right now, its overall flavour is an intrinsic, permanent quality of how it was baked. We use ser (é) for permanent characteristics, rather than estar (está) which is for temporary states.

Does ótimo change its ending depending on the subject?

Yes! Ótimo acts as an adjective describing o sabor (the flavour). Since sabor is a masculine singular noun, ótimo takes the masculine singular ending -o. If you were talking about a sopa (the soup), you would say ótima.

Is ótimo the same as saying muito bom?