The length of simmering time varies greatly on how much time you have to prepare the lasagna, and how much flavor you are wanting. As the sauce simmers it develops flavor. The longer it sits, the most flavorful your lasagna will be. You will want to simmer for a minimum of one hour to obtain the flavor we are creating in this lasagna. But if you have the time, and want the maximum flavor results, you can simmer for up to four hours. Another option for simmering the sauce for a longer period of time is to use a slow cooker. A slow cooker will allow you to set the sauce and go on about your day.