Combine the sliced apricots, granulated sugar, lemon zest, lemon juice, thyme sprigs, and kosher salt in a bowl and stir well to coat all the fruit evenly. Cover and refrigerate for at least 2 hours (or up to overnight). This maceration step is crucial—it draws out the apricots' natural juices and begins breaking down the fruit, which will help your preserves set properly and develop deeper flavor. I find that this resting period makes a noticeable difference in both texture and taste, so don't skip it even if you're short on time.

Pour the macerated fruit mixture (including all accumulated juices) into a heavy-bottomed pot and bring to a boil over medium heat, stirring occasionally. As the mixture heats, foam will begin to rise to the surface—this is normal and should be skimmed away with a spoon or small ladle. Continue stirring and skimming for about 10 minutes until the fruit breaks down significantly and the mixture becomes glossy and translucent. The apricots will soften and release their pectin, which will help the preserves thicken.

To check if your preserves have reached the correct thickness, place a small spoonful on a cold plate and put it in the freezer for 1 minute. Remove it and push gently with your finger—it should wrinkle slightly and move slowly if it's at the right consistency. If it feels too thin and flows easily, continue cooking for another 1-2 minutes and test again. I like to test a minute or two before I think it's ready, since overcooking preserves can make them rubbery and diminish the fresh fruit flavor.

Remove the pot from heat and stir in the vanilla bean paste until fully incorporated, which adds a subtle depth and complexity to the preserves. Return to a boil for just 1 minute to ensure the vanilla is fully integrated, then remove from heat. Discard the thyme sprigs using a slotted spoon or tongs—they've done their job infusing the preserves with subtle herbal notes.

Carefully pour the hot preserves into clean, sterilized jars, leaving about 1/4 inch of headspace at the top. Allow the jars to cool to room temperature, then cover and refrigerate. The preserves will continue to thicken slightly as they cool, so don't be alarmed if they seem a bit loose when first jarred.