Steam the barramundi for 8 minutes, or until fully cooked. Transfer to a serving platter.

In a heatproof bowl, combine the coconut cream, calamansi juice, patis, brown sugar, salt, ginger powder, and black pepper. Mix well and set aside.

To make the brown butter, melt the unsalted butter in a saucepan over low heat. Cook for about 7 minutes, or until it turns an amber color. Do not discard the browned milk solids, as they add flavor. Pour the brown butter into the coconut cream mixture and stir until well combined.

Add the tomato paste and cook for 5 minutes over medium-high heat. Add the chopped tomatoes next and 1/2 cup of the reserved mushroom liquid. Bring to a boil over high heat. Once boiling, reduce the heat to low, season with 1/2 tsp salt, cover, and simmer for 20 minutes. Stir from time to time to mash the tomatoes.