For the best flavor, use high-quality Gruyere and Parmesan cheeses. Toasting the walnuts enhances their nutty flavor and adds a pleasant crunch. Be careful not to overmix the dough, as this can result in tough scones. If you don't have fresh sage, you can substitute with 1 teaspoon of dried sage. These scones are delicious on their own, or served with a dollop of crème fraîche or a drizzle of honey. Scones are best on the day they are baked.