Place a medium saucepan over medium heat and pour in the kefir.

Heat gently for about 10 minutes, lowering the heat to medium-low if it starts to boil. The kefir should bubble lightly but not vigorously. Curds will begin to separate. Stir gently with a spoon. The more you stir, the smaller the curds will become.

Once a good amount of curds forms, stop stirring and allow the mixture to sit and thicken. When the whey takes on a slightly green hue, remove from heat. Add a pinch of salt and let it rest for 5-10 minutes.

Strain the mixture through a fine mesh strainer or cheesecloth over a bowl for 5 minutes. Transfer the ricotta to the refrigerator and chill for at least one hour or overnight.

While the ricotta chills, heat olive oil in a skillet over medium heat. Toast sourdough slices until golden brown on both sides. Remove and set aside.

Place chilled ricotta into a food processor or blender. Add olive oil and olive brine, then process until smooth and whipped.

Spread the whipped kefir ricotta evenly over the toasted sourdough. Layer with tomato slices and thin avocado slices. Finish with a sprinkle of flaky salt. Serve immediately.