Microwave the raspberries, sugar and water until the raspberries start to melt and the resulting liquid starts boiling. How long this takes will depend on your microwave and the temperature of your berries. My frozen raspberries took about 3 minutes in my microwave, but fresh raspberries will take less time.

Stir in the lemon juice and then dump the raspberries into a blender or food processor. Give the coulis a couple short pulses to puree the fruit, but be careful not to overdo it as the seeds will break up small enough to pass through the sieve which will result in a gritty raspberry sauce.

Pass the pureed raspberries through a fine-mesh sieve using a silicon spatula and collect the coulis in a bowl below.