Take your starter out of the refrigerator and let it sit on the counter. Let it warm up (you could leave it out a few hours, or even, overnight).
Pour off the hooch from top leaving a thin film.
Use a wooden spoon to stir it all together.
Place ½ cup of the stirred together starter into a clean container. Set aside the rest of the starter and you could use it in a sourdough discard recipe (or you could toss this discard out).
Add into the container with the starter a scant cup of flour and ½ cup of filtered water. Stir together to combine.
Close your container and place it in the warmest spot of your kitchen (I put the top on my jar but I don’t seal it closed).
After a few hours, close the container tightly and place in the refrigerator. The next day, your starter should be very bubbly and happy. Mark the height of your container to keep a better track of how it’s rising.
In case it’s not bubbly the next day, use a wooden spoon to stir the starter together. Remove most of the starter, leaving about a ½ cup.
Add into your container a scant cup of flour and ½ cup of filtered water (room temp to lukewarm). Stir together to combine. Leave on the counter (I leave on the counter with the jar lid loosely on top) for a few hours and then transfer to the refrigerator (seal the jar tightly).
The next day, your starter should be bubbling and ready. In case it is not, repeat the process one more time.
As soon as your starter is at its peak activity, it’s ready to bake with.