Why does a cake recipe call for 2 tbsp of hot water? This is my sponge cake recipe, I would like to know why add the  2 tbs of hot water

4 egg separated
1 tsp vanilla essence
3/4 cup caster sugar
1/2 tsp
bicarbonate of soda
1 tsp cream of tartar
3/4 cup cornflour
1 tbs
custard powder
2 tbs hot water
1 pinch salt
1 tsp icing sugar
1
tsp cornflour

Here is the method:

Prepare 2 x 20 cm deep round cake tins. Grease with butter and dust with combined icing sugar and cornflour
Preheat oven to 180C (356F)
Add vanilla to egg yolks.
Sift all dry ingredients, except salt and sugar, twice.
Beat egg whites and salt until stiff. Gradually add sugar. Beat in yolks.
Fold in sifted dry ingredients, THEN ADD THE 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.