Wash raspberries thoroughly and remove any stems or debris. Gently pat dry with paper towels.

In a large bowl, mash the raspberries with a potato masher until you have 4 cups of mashed berries. Leave some chunks for texture if desired.

Combine the mashed raspberries, sugar, and lemon juice in a large, heavy-bottomed pot. Stir well to combine.

Heat the mixture over medium-low heat, stirring frequently until the sugar dissolves completely.

Increase heat to medium-high and bring the mixture to a rolling boil. Continue boiling, stirring occasionally to prevent sticking or burning.

Boil the jam for approximately 15-20 minutes, or until it reaches the setting point. To test for doneness, place a small amount on a chilled plate - it should wrinkle when pushed with your finger.

Remove from heat and skim off any foam that has formed on top.

Ladle the hot jam immediately into sterilized jars, leaving 1/4 inch headspace. Wipe the rims clean, then secure the lids and rings.

Allow jars to cool completely at room temperature (about 8 hours). You'll hear a 'ping' sound as the lids seal.

Store sealed jars in a cool, dark place for up to 1 year. Once opened, refrigerate and use within 3 weeks.