Fill a canner with hot water. Place four 8-oz. jars in the canner. Bring water to a boil for 10 minutes to sterilize jars. Remove with jar tongs and invert on a rack.

Warm 4 cups (800 g) granulated sugar in a 250°F (120°C) oven for 15 minutes to help it dissolve.

In a saucepan, bring 4 cups (480 g) raspberries to a rolling boil while mashing them. Boil for 1 minute while stirring. Add warm sugar and boil for 5 minutes until thickened.

To test jam consistency, dip a spoon in the mixture; it should drop thickly. Before jar filling, heat lids in boiling water.

Fill jars with jam, leaving 1/2 inch headspace. Remove air bubbles with a spatula. Wipe rims and place lids; screw bands until fingertip tight.

Process jars in boiling water for 5 minutes.

Cool jars at room temperature for 24 hours. Ensure seals are tight before storing in a cool, dark place.