Combine the lemon juice and fruit in a heavy-bottomed saucepan and cook on medium heat for about 7 minutes while it breaks down and releases its juices.
Once it is boiling and juicy, add the sugar and zest, turn down to medium-low and continue to boil and reduce for another 15 minutes or so. You’ll feel as you mix it that the liquid is reducing and you’ll see on the sides of the pan that the level goes down about 1 inch in volume (depends on the size of your pan of course). As you mix occasionally, skim off the white foam that appears.
It’s done when it is visibly thicker and all the fruit is broken down. Add the orange liqueur, if using, right near the end. As the jam cools, it will thicken further.
Transfer it to clean, sterilized glass jars, let it cool a bit more, and then refrigerate. You’ll need to use it up in a week or two.
Since I made this jam way back in 2012, I've tried different methods - all yield good results. Here I let the fruit release some juices in the pan, then add the sugar and zest. You can also mix it all together before you start cooking it and let it sit on the counter or in the fridge. Or you can add all the ingredients except for the liqueur right at the beginning of cook time.
Have more apricots and less raspberries? Don't worry. Just follow the same basic instructions. As long as your total amount of fruit is about the same, it will be fine. Or double all the ingredients and make even more!