How to Make It
Stir together sugar, lemon juice, thyme, and 1 1/2 cups blueberries in a large saucepan over medium; bring to a simmer. Reduce heat to medium-low, and continue to simmer until blueberries are very tender, about 10 minutes. Let mixture cool. Discard thyme sprigs.
Transfer blueberry mixture to a blender, and process until smooth, about 30 seconds.
Pour blueberry sauce into a medium bowl, and fold in remaining 1 1/2 cups blueberries.