Add the lemon juice to a medium bowl. Pour the milk on top and stir. It should curdle pretty quickly. This is the "buttermilk."
In a large bowl, add the flour, baking powder, salt, and sugar and whisk well to combine.
To the buttermilk, add the room temp vegan sour cream and vanilla. Use an electric mixer on low speed until mostly smooth (it’s okay if there are very tiny crumb-size pieces of sour cream).
Melt the vegan butter in the microwave or in a small saucepan. Drizzle it into the wet ingredients and mix until combined and no lumps remain (see Note 4).
Pour the wet ingredients over the flour mix. Fold with a wooden spoon until just combined. Do not overmix—lots of lumps are fine. Rest the batter for 5 minutes (or 10 minutes). The batter will be very very thick and fluffy, almost like a yeast bread dough. But don't stir after resting—the batter will lose air bubbles, resulting in a flat pancake. Preheat the pan. Heat a nonstick frying pan over medium heat for several minutes. Add a teaspoon of coconut oil (see Note 5). Allow to heat ~30 seconds. Test to see if the pan is hot enough by adding a droplet of water—if it sizzles and dances, it’s ready. Cook the pancakes. Ladle a heaping ⅓ cup pancake batter into the pan (since the batter is thick, it won’t ladle into a perfect circle). For smaller pancakes, use a heaping 1/4 cup batter. After the first 20-30 seconds, swirl the oil in the pan around the pancake edges to get those crispy edges. Cook for a total of 2 to 2 1/2 minutes, until the edges start to dry out and you can see the bottoms are golden brown. Carefully flip. Cook on the second side for a total of 2 to 2 ½ minutes, swirling any remaining oil around the edges again.NOTE: don’t flip back and forth, just the one time. This makes pancakes less fluffy without a uniform golden brown exterior. Repeat with the batter, adding a teaspoon of oil to the pan to preheat per pancake before adding more batter. Reduce the heat as you go to prevent burning (my burner is 1 to 7; I start at 4 for the first pancake, then reduce to 3).
To keep pancakes warm, add to a wire rack-fitted sheet pan in the oven at 200ºF/95ºC until ready to serve. Serve pancakes warm with maple syrup and a pat of vegan butter, if desired. If you have leftover batter, store in an airtight container in the fridge for 5 to 6 days.