Place a strainer over a small bowl, and pour half the defrosted raspberries into the strainer. Using the back of a spoon, press the juice out of the raspberries and it will strain into the bowl.
When all the juice is pressed through, pour the raspberries into another bowl or throw away. Then strain the other half using the same method. (I make a smoothie with the raspberries after, I don't throw them away. Just an idea!)
When you're done straining the raspberries, add the lemon and agave and stir.
Add a tablespoon of the pressed raspberries back into the sauce and stir. This will add some texture to the sauce. If you like it smooth, then just leave it out.
Pour into a jar, and chill in the refrigerator. Makes about 2/3 cup.