Preheat oven to 400°
Par-boil the sausage in boiling water for 15 minutes.
Heat butter and oil in an oven-safe skillet.
Add the grapes and fresh basil to the skillet and cook on medium-high heat for 3-4 minutes, just to incorporate the flavors.
Nestle the par-boiled sausages between the grapes.
Place the skillet in the oven for 40 minutes, flipping the sausages at 20 minutes.
After 40 minutes in the oven, remove the skillet and place it on a stovetop burner.
Remove and discard the cooked basil leaves.
Remove the sausages from the skillet and set them aside on a plate.
Add the balsamic vinegar to the grapes and cook on medium heat for 3-4 minutes.
Place the sausages back in the skillet and cook for 3-5 minutes to reheat the sausages.
Garnish with fresh basil leaves.