Both lemon meringue and key lime pie have bright, creamy, and acidic flavors. But, there are some significant differences between the two recipes. For one, key lime pie is made with key limes, while the other uses less tart lemons. The cooking processes are also very different. For lemon meringue, cook the flour, lemon juice, sugar, and egg mixture on the stovetop, make the meringue separately, and then bake them together. In contrast, key lime pie is mixed in a bowl and poured into the crust to bake in the oven.