Im not sure what "restaurant level" means. But, corn soup is only as good as the corn that you use to make it.
Here's a quick and dirty recipe.
4 Tbsp butter;
6 ears fresh picked corn;
6 to 8 cups quality chicken broth or stock;
1 cup shallots, minced
1/2 white or yellow onion, minced
Fresh ground black pepper
Fresh picked herbs of your choice to garnish
With a sharp knife, remove the kernels from 5 of the 6 ears of corn making sure only to cut the crowns leaving the hulls on the cob. Reserve one whole cob. Turn the knife over and using the top of the blade, scrape the cob to remove the remaining kernels and the corn "milk." Break the cobs into thirds and reserve.
In a large pot, melt the butter. Add the shallots and onion with a healthy pinch of kosher salt. Saute until the onions are soft and translucent; about 8 to 10 minutes. Add the broth, kernels, broken cobs and whole ear of corn to the pot. Bring to a generous boil and reduce heat to a gentle simmer. Cook for 10 minutes. Remove the whole ear of corn and set aside. Let simmer for another 10 minutes, remove the broken cobs and discard.
With an immersion blender or food processor, puree the soup until very smooth. Strain the soup through a fine sieve into a large bowl, pushing the liquid through with a ladle or rubber spatula until nothing but the fibrous bits are left behind. Discard what's left in the sieve.
Return the soup to the stove over low to medium heat. The soup should be creamy. If too thick, add more broth. If too thin, let reduce until it reaches the desired consistency. Remove the kernels from the last ear of corn in the same way as before. Add the kernels and the corn "milk" to the soup. Gently simmer for 5 to 7 minutes or until the kernels are just soft. Taste for seasoning and adjust accordingly.
Ladle into warm bowls and garnish with fresh picked herbs.
For a more spicy end product, add a diced jalapeno or similar pepper with the kernels from the last ear of corn, seeds and ribs removed or add a pinch of Cayenne or white pepper. I prefer the peppers.
For a "smoky" twist, dice 2-3 strips of thick cut smoked bacon, fry separately and add with the kernels from the last ear of corn.
The variations are endless, but a basic corn bisque is pretty simple.
I cut fresh kernels off the cobb, and use the back of the knife to scrape the cobb and "milk" all the juice and pulp from the cobb.
Cover cobbs with cold water and bring to a low simmer. Simmer for about 30 minutes, remove from heat, allow to cool and strain.
Sweat some onion and leek in butter...try to get a good sweat, add some salt to the vegetables in the beginning to promote water loss. You want nice wilted, translucent vegetables. Then add the corn (and scrapings from the cobb) to the pot. Sweat the corn for about 5 more minutes, then add the corn stock (you could first add a little white wine if you wanted, just make sure to cook off alcohol before you add stock) and any herbs if you want. I like thyme or tarragon. Tie herbs in a satchet and cook until corn is quite tender, probably 30-45 minutes.
Blend until very smooth, and pass through a fine mesh strainer. Add cream, lime juice, salt and pepper to taste. I personally don't like a LOT of cream (I think it sometimes dulls flavors) but YMMV. I also adjust consistency at this point, adding more corn stock, cream, lime juice, or even water until the flavor/consistency is where I want it. IMO people often make soup too thick, which I don't like. But again, you can adjust how you want.
Garnish can be anything as well. Quick pickled corn, chilis, crab, lobster, corn salsa, fine herb mix...