Set a fine mesh sieve over a mixing bowl, and have it near your stove.

Place the blackberries, sugar, and water in a small saucepan. Squeeze the lemon juice into the pan, and stir to combine.

Cook the mixture over medium heat for about 10 minutes, stirring occasionally. The blackberries will begin to break down as they cook, and you can gently smash them to help the juices release.

When the coulis is ready, the mixture level should be slightly lower in the pan, and the juice should drip a bit slowly off the end of a spoon. After cooking, pour the mixture into the sieve and gently press it with a spoon to get as much of the coulis out as possible.

After it’s cooled, store the coulis in an airtight container or jar. it can be kept in the refrigerator for one week, or in the freezer for up to three months.