Lemon's popularity with bakers is due in part to its gratifying ability to play nicely with other flavors. For example, a lemon cake mix can quickly be improved by adding raspberries to the batter. The raspberries broaden and deepen the relatively one-note tang of the lemon, while the sweetened lemon flavor of the cake mellows the raspberries' acidity. It's a quick and easy dessert, though a few minor adjustments are helpful.
Two Quick Tips
Packaged cake mixes are designed to create a cake with a light, delicate crumb, so they tend to make relatively thin and wet batters. These aren't ideal when you're adding berries or diced fresh fruit, which have a tendency to sink and form a sodden layer at the bottom of the pan. There are a couple of ways to counter this. One is to place your raspberries on top of the batter when it goes into the oven, so they'll sink into place in the middle of the cake as it bakes. A second alternative is to reduce the liquids in the cake by a tablespoon or two, which thickens it slightly and compensates for the juice the raspberries release.
Using Fresh Berries
If you're adding fresh raspberries to your cake, pick them over carefully to remove any that are moldy or insect-damaged. Rinse them under cold water in a colander, drain them well, and gently roll them on a paper towel to dry them. The top-of-the-batter trick works well with fresh berries, but you can also stir them into the batter after it's mixed so the berries don't leave a red blotch on the surface of the cake. If the berries are tart, roll them in powdered sugar first. It sweetens them lightly, and also helps keep them from sinking in the batter.
Using Frozen Berries
Raspberries have a relatively short season, and out-of-season supermarket berries are often disappointing, so often frozen berries are your best option. They're usually picked much closer to their peak of ripeness, and then quick-frozen to preserve that fresh flavor. Frozen berries release their juices more quickly than fresh berries, so toss them in flour, cornstarch or a mixture of flour and powdered sugar to absorb some of the juice. Stir them gently into the batter at the very end, adding them in small quantities so they don't freeze a section of batter into a solid lump.
The combination of lemon cake and raspberries is wonderful on its own or frosted with plain white icing, but there are several ways to make it more elegant. To serve with tea or coffee, place a paper doily on the cake and sift powdered sugar over it. Lift the doily away to reveal the pattern. Alternatively, make a layer cake and fill the middle with lemon curd or raspberry preserves. When sliced, it makes for a dramatic presentation. The berry-filled cake can also be baked in a loaf pan, making a slightly denser cake that can be glazed on top with a mixture of lemon juice and granulated sugar.