If you have a good recipe for lemon curd and want to make it, go for it. If you're planning on purchasing it, like I did for this cake, give it a taste before you use it and consider how tart it is. Having a tart lemon curd between the layers of this cake is pretty important, in my opinion, because it balances out the sweetness of the cake and blackberry buttercream. If your lemon curd doesn't have a pronounced tart lemon flavor, adding in a bit of lemon extract or lemon oil can make a big difference in the finished flavor of your layer cake.My favorite brands of prepared lemon curd are Dickinson's and Bon Maman.