• You can see the steps in images in the post.

Macerate the raspberries:

• Carefully pour the raspberries into a large bowl filled with water to remove any impurities, then drain quickly.
• Drain them thoroughly, then place 650 g (22.9 oz) in a large, tall pot.
• Finely blend the remaining raspberries, then strain through a sieve to remove the seeds.
• Add this coulis to the raspberries in the pot, then add the sugar and lemon juice.
• Note: If you don't mind the seeds, use the whole raspberries without reducing any of them to a coulis.
• Mix well to coat fruit with sugar.
• Cover and leave to macerate for at least 2 hours. Preferably leave overnight in the fridge. This resting time allows the raspberries to release their juice and the sugar to melt.

Sterilize jars:

• Sterilize the jars just before starting to cook the jam.
• Wash jars and lids in hot, soapy water, then rinse well.
• Place them and the lids in a pot and cover with hot water.
• Boil for 15 minutes.
• Remove from the water with tongs and drain upside down on a clean cloth.
• You can also sterilize them in an oven preheated to 140°C (285°F).

Cooking raspberry jam :

• 1 hour before cooking, place a small plate in the freezer. It will be used to test for baking.
• After the maceration time, place the pot over high heat and bring the mixture to the boil, stirring regularly.  Quick cooking in a large pot preserves the fruit's vitamins and color.
• Once the jam starts to boil, cook for 12 to 15 minutes. Add the knob of butter as soon as the foam begins to form. Butter will prevent scumming. If you still have a little, remove it towards the end of cooking with a skimmer.
• After 8 minutes of heavy bubbling, lower the heat slightly to avoid spattering and to better control the end of cooking.
• Stir frequently to prevent the jam from sticking to the bottom of the pot.
• Cooking time will depend on the juice of the raspberries and the intensity of the heat.
• The jam is ready when it coats the spoon well. You can also do the plate test. Spoon the jam onto the plate you've put in the freezer.
• Leave to cool for a few seconds, then tilt the plate. If the jam sets and does not run easily, it is ready. If not, continue cooking for a few more minutes.
• Remove from heat and immediately fill sterilized jars almost to the brim. Use a funnel to avoid dirtying the jars. If this happens, after closing them, clean them with a damp cloth.
• Close the jars by screwing the lids on tightly, then turn them out onto a towel.
• Let cool completely before turning them right side up.