Pick through the raspberries and remove any that are discolored or bruised. Rinse them well and drain them well in a colander. Make sure you don't leave them sitting in water too long because the raspberries will start to absorb water.

Combine the sugar, lemon juice, and rinsed/drained raspberries in a heavy-bottomed saucepan. Cook over medium heat until the sugar is dissolved.

Once the sugar is completely dissolved, increase the heat to medium-high and bring to a rolling boil. Boil for two minutes, stirring constantly (it will foam up as it boils).

Turn the heat to medium-low to maintain a simmer. It is important to keep the mixture continuously simmering for 20 to 30 minutes so that it will reduce and thicken. Stir often, scraping the bottom to avoid the jam sticking. Use the back of a large wooden spoon to gently smash the raspberries to a smoother jam-like consistency as you stir.

When the jam reaches 105 degrees C / 221 degrees F, remove it from heat. If you don’t have a candy thermometer, then place a plate in the freezer to get very cold. Place a small amount of the jam (1 tsp.) on the freezer plate and place the plate back in the freezer for a few minutes to cool. If the jam seems very close, then remove it from the heat while the plate is in the freezer to wait to see if it is done. If the jam wrinkles when pushed with your finger, the jam is done; if not, return to a boil for 5 min. and repeat. Be careful as the jam thickens, it can start to burn, so stir more frequently.

Pour the jam into warm sterilized jars leaving 1/4 inch headroom at the top. Use a sterilized spoon or knife to gently stir the jam in the jars to remove air pockets.

Clean the rims of the jars with a clean, warm, wet cloth. Place lids on and screw to tighten until finger-tip tight only. Place in a water bath canner and process for 10 min. or according to altitude.

When the jam has cooked for its allotted time, remove the jars to a towel-lined counter to cool. You should hear the popping of the lids as they seal. If any jars don't seal, refrigerate and eat right away or freeze.