In a large pot, warm the olive oil over medium heat. Add the onion, carrot and celery. Sprinkle with salt and cook for 5 minutes, until onion is translucent and veggies are slightly soft.
To the pot, add the apples, thyme, garlic and ginger. Cover and cook, stirring often, for 15 minutes, until apples have broken down and vegetables are starting to brown.
Pour in the broth and bring to a boil. Reduce to a simmer and cook for another 15 minutes, until vegetables are soft. Remove from heat and allow to sit for a few minutes.
Transfer the soup to a blender and blend on high until smooth. Alternatively, you can use an immersion blender and blend in batches until smooth. Add more broth if you prefer a thinner texture.
Combine yogurt and maple syrup in a small bowl. Serve warm garnished with yogurt and fresh thyme (optional), and enjoy!