Preheat your oven to 350°F (175°C). Lightly grease an 8x8-inch baking pan or line it with parchment paper for easy removal.
In a large mixing bowl, whisk together the flour, sugar, cocoa powder, salt, and baking soda until well combined.
Make three small wells in the dry mixture. Pour the vanilla extract into one, the vinegar into another, and the vegetable oil into the third. Then, pour the water over everything and stir until just combined. Do not overmix.
Pour the batter into the prepared baking pan and smooth out the top. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool completely before frosting.
For the frosting: In a medium bowl, beat together the softened butter and cocoa powder until smooth. Add the honey (or Karo syrup) and vanilla extract, mixing until combined. Gradually add the confectioners' sugar, alternating with heavy cream (or milk), until you reach a smooth, spreadable consistency. Add a pinch of salt to enhance the flavors.
Once the cake has fully cooled, spread the frosting evenly over the top. Add chocolate sprinkles, if desired, and enjoy!