I am putting this in the general baking category because it can be used for so many things including cakes, cookies, ice cream, donuts, etc. The berries don't have to be thawed. They can be used either way.
Depending on how thick you want this and what it will be used for, you can adjust the cornstarch between 4 and 6 Tbsp.
2 12-ounce packages of frozen raspberries (IQF, not packed in syrup)
1 1/3 cups water
1 1/2 cups sugar
2 tbsp lemon juice
5 tbsp cornstarch dissolved in 1/2 cup of water
In a medium saucepan combine the raspberries, water, sugar and lemon juice and bring it to a boil stirring occasionally. Turn down heat and simmer for 15 minutes or the raspberries have broken down.
Remove from the heat and strain with a fine mesh sieve (or cheesecloth) into a clean pot and return to heat. Mix the cornstarch in 1/2 water then add some of the hot syrup to it. Pour this into the pot of syrup and stirring constantly, bring back to a boil. Reduce heat and simmer, stirring occasionally, until it is thickened and clear about 5 minutes.
Remove from heat and cool completely. Filling may be transferred to a heat resistant bowl or container uncovered until cool. It will may take awhile to set up like jelly.
Yields 3 1/2 cups