Place the apples and blueberries into a heavy bottomed pot large enough to hold all the ingredients and allow room for stirring.
Add just enough water to cover the bottom of the pot–about 1/2 inch of water on the bottom or so.
Put the pot onto high heat and stirring constantly, bring to a boil.
Turn heat down to medium, and stirring continually, cook until the apples are all soft and some are beginning to break down, thickening the released fruit juices.
Stir in the sugar and spices and keep cooking until the sugar is well combined.
Turn off the heat, but keep the pot on the stove in order to keep the applesauce hot.
Using an immersion blender, a food processor or food mill, grind the fruit up into a slightly chunky puree–or, if you wish, grind it down to a perfectly smooth puree.
Stir in the lemon juice thoroughly, then pack into hot pint or quart jars.
Try to get any visible air bubbles out with a spatula; this is very difficult with very thick foods like applesauce, but try anyway. Wipe off the rim of the jar with a damp cloth, then center a lid on top and screw on a band.
Do not tighten the band–just screw it down until it is closed, but not at all difficult to unscrew.
Put into a hot water bath canner, making certain that water covers the jars completely.
Bring to a boil, clap the lids on top of the canner and process the jars for 20 minutes–the processing time is the same for either pints or quarts.
When they have processed for twenty minutes, turn off the heat and open the lid to the canner.
Allow the jars to sit in the hot water for five minutes, then carefully lift up each jar and set it on a folded dishtowel in order to keep the counter from possibly cooling the glass too rapidly, causing the jar to crack.
Check the seals on the lids–they should be concave and very tightly adhered to the jar rim.
If after 24 hours the lids have not sealed, either use up the food that did not seal, or re-pack using new jars and new lids.