- Preheat the oven to 375 °F (190 °C). Grease eight 1-cup (250 mL) soufflé dishes and sprinkle them with sugar, tapping out any excess and placing them onto a baking tray.
- Bring the raspberry puree and sugar up to a boil in the saucepot and boil the mixture without stirring until it reaches 242 °F (117 °C) on a candy thermometer, about 5 minutes from when the mixture starts to boil.
- While the raspberry syrup is cooking, whip the whites with the cream of tartar until foamy. Once the syrup reaches temperature, carefully pour it down the side of the mixing bowl (to avoid splashing) into the egg whites while whipping, then increase the speed to high and continue to whip until the whites hold a medium peak when the beaters are lifted. Fold in the lemon juice, vanilla, and Chambord or other raspberry liqueur.
- Gently spoon the soufflé mix into the prepared cups to fill just halfway and bake for about 20 minutes, until they have doubled in size and are just beginning to turn golden on top. Serve immediately.