Heat oven to 350 degrees F. Line the bottom of 9-inch round cake pan with a fitted round of parchment paper and coat the bottoms and sides with nonstick cooking spray. Whisk together flour, baking soda, salt and granulated sugar in the bottom of a large mixing bowl. Add coconut oil, coconut milk, and vinegar and whisk until batter is smooth. Pour into prepared pan. Bake for 25 to 30 minutes, or until the top is springy and a tester inserted in the center comes out batter-free. Cool the cake in the pan on a wire rack for 10 minutes, then cut around it with a knife to ensure it is loosened and flip it out onto a cooling rack to cool the rest of the way. If you wish to make a glaze: Whisk together 3/4 cup powdered sugar with 1 to 2 tablespoons of the leftover coconut milk, adding a little at a time, until it is smooth but not too runny. Add a pinch of salt, if you wish. Once cake is fully cool, spread over the top of the cake and smooth to the edges with a knife or small offset spatula, where it will find its way down the sides decoratively on its own. I added some white confetti sprinkles, but toasted coconut chips would be nice here too.