Clean the spinach well until all dirt particles are removed and dry.
In a wide pan over medium heat add the butter, oil and cook the onions, garlic until translucent. Add the tarragon and thyme and mix well.
Add the spinach to the pan and place the sea bass on top of the spinach.
Add the wine, lime juice, salt and pepper nicely the sea bass.
Cover with a good fitted lid and cook until the fish is cooked, 5 minutes. It should be springy to the touch.
Remove from the heat and place in a plate. Reduce the sauce remaining in the pan and add the heavy cream and more salt and pepper as desired.
Pour the sauce over the fish and spinach.