Apple Upside-Down Cake

Buttery cake and caramelized apple sounded like a perfect match. Well, it was what I dreamed at the beginning. I don't exactly remember which recipe I partially adapted and how I twisted it. The result was, to be honest, disappointing. The cake part was dense; the apple part was too sweet. I think that I reduced sugar too much from the cake part (again), but I must have skipped a good amount of sugar from the caramelized apple, too. How could the apple layer still be too sweet?

First, I guess that a type of apple I used here (Jazz = too sweet for baking) was wrong. Second, caramelizing didn't happen enough. So, there wasn't a deep and bitter caramel flavor, which would nicely offset sweetness. I might have reduced not only sugar but also butter for apple layer and have not cooked until caramelizing apple. I will try again with proper sour apples and almost stick to a trusted recipe.