½cupMexican crema, or 1⁄4 cup cultured buttermilk and 1⁄4 cup heavy cream
Juice of 1 lime
½teaspoon black pepper
Put the mayonnaise, crema, lime juice, and pepper in a bowl and whisk. Add the salt, adjusting to taste, while whisking as needed. The final sauce should be thin enough to easily spoon (or to dispense from a squeeze bottle as they do at the taco stands) but thick enough that, once dispensed, it sits firmly in place and doesn’t run off the fish.
If you need to make it thinner, add lime juice, or crema. Alternatively, to make it firmer, add mayonnaise or heavy cream. Serve in a squeeze bottle or in a bowl with spoon. White sauce will keep in the fridge for up to 1 week.
The Taste Edit - Baja White Sauce https://thetasteedit.com/baja-beer-battered-fish-tacos-with-cabbage-and-white-sauce/