Adjust oven rack to middle position and heat oven to 350 degrees. Coat 8-inch-square baking pan with nonstick cooking spray. Add the flour, sugar, cocoa, baking soda, and salt together in the same pan.
Make 1 large and 2 small craters in dry ingredients with a spoon. It need not be perfect.
Add the oil to large crater
and vinegar and vanilla separately in the small craters.
Now pour water into the pan,
and mix until just a few streaks of flour remain. DO NOT OVERMIX.
Immediately put pan in oven. Bake until toothpick inserted in center of cake comes out with a few moist crumbs attached, about 20-30 minutes depending upon your oven.Though it looks pretty dry in this photo, it was in fact deliciously moist!
Cool in pan, then dust with confectioners’ sugar. Or serve it on a plate with dusted sugar and berry garnish.