You can substitute the unsalted butter with coconut oil or a vegan butter alternative for a dairy-free version. Optional variations include adding nuts, such as walnuts or pecans, or swirling in some peanut butter or caramel for a unique flavor twist. Store leftovers in an airtight container at room temperature for up to three days or freeze for up to a month. Reheat slices in the microwave or warm oven before serving.