In a large mixing bowl, combine apricots, sugar, and 3 tablespoons lemon juice and mix until all the sugar is moistened; if some sugar remains dry, allow to macerate until fruit has released enough juices to moisten sugar, about 5 to 15 minutes minimum. This will help prevent the jam from scorching and allow the natural pectin to be drawn out.
A note on maceration time: Though not absolutely necessary, increased maceration times will improve the taste of your jam. After 1 hour of maceration time at room temperature, you can cover and store the fruit in the refrigerator for as long as 7 days. Stir macerating fruit once or twice a day until ready to proceed.
Scrape apricot mixture into a wide shallow pot and heat over medium-high heat, stirring regularly, until sugar is melted and mixture starts to bubble, about 10 to 15 minutes.
Set several metal spoons on a plate in the freezer.
Heat apricot mixture over medium-high heat, stirring as needed to prevent scorching, until jam starts to foam, about 15 minutes. Continue to cook, stirring minimally and lowering the heat if necessary to prevent scorching, until foaming has subsided, about 15 minutes longer. Scrape any foam off jam surface with a stainless steel spoon as needed.
Taste jam for tartness: If the jam tastes too sweet without a good balance of tartness, add 1 tablespoon of the remaining lemon juice at a time, stirring well and tasting between additions, until the lemony flavor is just barely perceptible and the balance of sweet and tart has been reached (like a good lemonade). Do not leave this step out as it also helps the jam to set.
Continue to cook until bubbling has slowed and jam looks glossy and appears thickened around the edge, about 5 to 15 minutes; lower heat as necessary to prevent scorching.
Turn off heat and set a dollop of jam on one of the freezing-cold spoons, then return to freezer for 5 minutes. Jam is ready once it holds together and doesn't run off the spoon when tilted. If jam is too runny, return to heat and cook, stirring frequently and repeating the spoon test every 5 minutes, until jam passes test.
Ladle hot jam into hot, sterilized jars, leaving 1/4-inch head space. Process 15 minutes in boiling water bath.