Heat medium skillet over medium heat. When pan is hot, add neutral oil and swirl to coat bottom of skillet entirely.
When oil is hot and shimmering, add chopped onion, minced garlic, and kosher salt. Stir well and cook, stirring constantly, until vegetables are soft and begin to brown, approximately 3 to 4 minutes.
Add 1 ½ cups black beans to skillet. Use back of wooden spoon or potato masher to mash beans completely, until no whole or partial beans remain.
Add remaining 1 ½ cups black beans and mash to preferred consistency.
Cook mashed beans, stirring constantly, until starches begin to coat bottom of skillet and turn golden brown, approximately 3 minutes.
Slowly pour in bean liquid in small increments, stirring well to incorporate liquid after each addition. Bring mixture to simmer over medium heat and cook, stirring and scraping bottom of skillet, until liquid is fully incorporated and beans are heated-through, approximately 2 minutes. Note: beans may look soupy but will thicken as they cool. Be sure to use entire ¾ cup of liquid to prevent beans from drying out.
Serve as desired with chips, tacos, or other entrée.