Wash 4 pounds of fresh crab apples under cool running water and pat dry, then halve each apple, removing stems and blossom ends.

Place the halved crab apples and 4 cups water into a large stainless steel pot and bring to a rolling boil over high heat.

Reduce heat to medium and simmer gently for 20 to 25 minutes, stirring occasionally, until the apples break down and become very soft.

Line a colander with cheesecloth and pour the cooked apples and liquid through it into a bowl; let the juice drip for at least 4 hours or overnight without pressing the solids.

Measure the strained juice; for every 1 cup of juice, prepare ¾ cup granulated sugar, then pour approximately 4 cups of juice back into the cleaned pot and stir in 3 cups sugar.

Over medium heat, stir the juice and sugar mixture for 2 to 3 minutes until the sugar dissolves and the liquid is clear.

Increase heat to high and bring to a rapid, rolling boil, then attach a candy thermometer and continue boiling until the mixture reaches 220°F (104°C), about 15 to 25 minutes.

While cooking, skim off any foam with a large spoon and sterilize jars and lids by boiling or using a hot dishwasher.

Once the jelly reaches 220°F, remove from heat and carefully ladle into warm sterilized jars, leaving ¼ inch headspace.

Wipe jar rims, apply lids and rings finger-tight, then let jars cool undisturbed for 12 to 24 hours until lids pop to seal.