Combine the mashed berries and sugar, cover and let macerate in the refrigerator for 2-24 hours.

When you're ready to make jam, pour the macerated berries into a medium-sized non-reactive pan. Bring to a boil and let the jam bubble, stirring regularly, until it reduces and develops a syrup-y look.

Using a candy thermometer, monitor the cooking jams temperature. When it reaches 220 degrees, remove it from the heat. If you don't have a thermometer, use the plate test to test the jam's doneness. To test the jell stage of the jam using plates, put a couple of small plates or saucers into the freezer before you begin to the make the jam. When you're ready to test your set, pull one of the plates out and drop a small dollop of jam onto the center. Let it sit for a minute or two. If the jam is ready, it will develop a thin skin that will wrinkle when gently nudged. If it just runs all over the plate, it needs a few more minutes of cooking.

When jam has reduced down and is finished cooking, remove from heat and add the lemon juice and zest, stir to incorporate. Ladle into prepared jars, wipe rims, apply lids and rings and process in a boiling water canner for 15 minutes, if desired. This jam will keep for a couple of weeks in the fridge without processing.