Preheat the oven to 350°F / 175°C. Lightly grease an 8in / 20cm square baking pan at least 2in / 5cm deep.
Whisk 1½ cups of all-purpose flour, 1 cup of sugar, ¼ cup of unsweetened cocoa powder, 1 teaspoon of baking soda, and ½ teaspoon of salt in a bowl.
In another bowl, whisk 1 cup of water, ⅓ cup of vegetable oil, 1 tablespoon of cider vinegar, and 1 teaspoon of vanilla extract. Stir into the dry ingredients until combined.
Pour into the pan and bake for 30-35 minutes, until a toothpick inserted in the center comes out clean. Let cool.
For the icing, melt 1½ cups of semisweet chocolate chips with ½ cup of half-and-half, stirring until smooth. Spread over the cooled cake.
