Why does a cake recipe call for 2 tbsp of hot water?
My sponge cake recipe has the same thing (though I think it has 1/2 dl water). It's basically because the person creating the recipe found that without it the cake batter was too thick and didn't yield a cake that was airy enough. When I left out the water, the cake became more dense and didn't rise quite as much. I find that that water is a nice place to add various flavours, like lemon juice or coffee by substituting some of the water.