Cook Raspberries: Into a pot add a bit of water, raspberries (no need to defrost frozen), sugar, and salt. Stir, put the pot over medium heat and bring to a boil, stirring every so often. Keep an eye on it at the beginning until the raspberries release their juices.
3 cups raspberries, 3 tablespoons white sugar, pinch salt
Adjust Flavor: Take the pot off the heat, add about half the lemon juice, then taste. If it needs more sweetness add a bit more sugar; if it could use more acidity add more lemon juice; or add a pinch of salt if the flavor isn't quite there. Balance the flavors until you're happy with them.
2 teaspoons lemon juice
Thicken With Slurry: In a small bowl combine cornstarch with water and stir until smooth to make a slurry. Pour about half of the slurry into the pot while stirring, return the pot to heat, and continue stirring until it thickens. If it's not yet fairly thick and spoonable, add another 1/2 to 3/4 of the remaining slurry and repeat; make more slurry if needed. Once it's thick enough, cook about a minute on low to remove any cornstarch aftertaste.
2 tablespoons cornstarch, 2 tablespoons water
Finish And Taste: Remove the pot from heat and taste one final time. Add a bit more sugar or lemon juice if needed to balance the flavor.
Store Or Refrigerate: Use the compote immediately, or let it cool and refrigerate in a sealed container.
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Notes
Nutrition information: the exact macros depend on how much sugar you add. Treat these values as a rough estimate.