Combine the dry ingredients: In a bowl, combine the dry ingredients (flour, sugar, unsweetened cocoa powder, baking soda and salt)
Add the wet ingredients: Pour in the wet ingredients (water, oil, vinegar, and vanilla extract). Whisk to combine.
Bake: Pour the batter into the lined dish and cook in the microwave for 8 to 12 minutes on high. (See notes on baking time)
The cake is ready when a toothpick inserted in the center of the cake comes out clean.
Stand for 5 minutes then use the overhang parchment paper to lift the cake out onto a wire rack and cool completely.
Once cool cut the cake into squares.
Freeze the squares for 30 minutes before dipping in the sauce. (See note on freezing cake squares)