Recipe Prep: Clean two 8-ounce jars with hot soapy water. Thoroughly rinse the jars and dry with a clean dish towel. Place a small plate in the freezer. This plate will be used to test if the jam has cooked enough. Cut each apricot into 6 wedges. You should at least 1 pound (454 grams) after the pits are removed.
Combine and Macerate: In the pot, combine the apricots, sugar, and lemon juice. Gently stir to combine. Let the mixture sit at room temperature for 2 hours, stirring occasionally. This will draw out the juices and flavor from the apricots and help dissolve the sugar.
Cook: Place the pot over high heat and bring to a boil. Once it starts to boil, reduce the heat to medium-high and cook stirring occasionally. The fruit should still be boiling.
Cook the jam until it reaches 217-220°F (102-105°C). This is the temperature at which the jam will set properly. At this point a lot of the liquid will have cooked off and the jam will be noticeably thicker. Use an instant-read thermometer to check the temperature.
Test for Set: Once the jam reaches at least 217°F, spoon a small amount onto the chilled plate that you placed in the freezer earlier. Return it to the freezer for a minute. If the jam wrinkles when you push your finger through it, it's ready. If not, continue cooking and test again in a few minutes.
Stir in Vanilla: Once the jam has reached the desired consistency, stir in the vanilla extract and then remove the jam from the heat.
Store the Jam: Let the jam cool for about 10 minutes, then transfer the jam to the clean jars. Let the jam cool to room temperature and then refrigerate for up to 2-3 weeks.
Canning the Jam: If you want to can the jam for longer shelf life, fill the jars but leave a 1/2-inch headspace. Follow these directions from Ball Jar Co. to safely can the jam.