Preheat the oven to 275 degrees.

Place the black bass fillets, skin side down, in a baking dish that comfortably fits them.

Drizzle 3 tablespoons of extra-virgin olive oil over the fish and season with sea salt.

Roast in the preheated oven for 15 to 25 minutes, or until the fish is just cooked through.

While the fish roasts, heat 2 tablespoons of extra-virgin olive oil in a large saute pan over medium-high heat.

Add the sliced shiitake mushrooms to the pan, season with salt, and saute until lightly browned and softened.

Transfer the sautéed mushrooms to a bowl, adjust seasoning as needed, and keep warm.

Return the saute pan to the heat and pour in the remaining 2 tablespoons of extra-virgin olive oil.

Add the thinly sliced shallots, peeled ginger slices, and diced rhubarb to the pan.

Cook, stirring occasionally to scrape up any browned bits from the pan, until the rhubarb begins to soften, about 4 minutes.

Add 3/4 cup of water and 2 teaspoons of sugar to the pan.

Season with salt.

Cook the mixture until the liquid has reduced by half.

Whisk in 2 tablespoons of butter and 1 tablespoon of heavy cream until smooth.

Stir in 1 teaspoon of balsamic vinegar.

Press the sauce through a fine-mesh sieve set over a bowl to create a silky texture.

To serve, divide the rhubarb sauce among 4 shallow bowls.

Lay a piece of roasted black bass in each bowl, atop the sauce.

Spoon a portion of the sauteed shiitake mushrooms over the fish.