Whisk the cornstarch, water, and cold yogurt until the cornstarch is dissolved. Add the salt until smooth.
Place over medium heat and whisk constantly, without stopping, until it reaches a full boil.
Lower the heat slightly and gently add the baked dumplings. Simmer, stirring occasionally and gently, for about 10 minutes, until heated through and starting to float.
In a small pan, sauté the garlic in oil until just starting to turn golden, add the pine nuts and toast until light golden, then stir in the mint for the final 30 seconds. Pour over the soup and serve hot.