Thick layer of egg formed at the bottom of sponge cake I've made several attempts on this recipe (the ingredients are on the video Description) and... I get the fluffiness of the cake and a great taste out of it once I throw in a bit of lemon or vanilla (whatever is available) to get rid of the egg smell but no matter what I do there's always a thin layer of eggs formed at the bottom. 

I've added more flour (20 grams more to the 60 grams, a total of 80grams) but it didn't really do much to it. 

I've whisked it the best I could, folded it as many times (10-15 folds)... I'm out of ideas sadly. I'm by no means experienced either so I just want to "perfect this" fluffy delight so I can finally make it properly. 

The ingredients are: 5 egg yolks and one egg, 60g butter, 100ml milk, 60g plain flour, 20g corn flour and 5 egg whites, 1/4 tsp salt, 80g sugar.

The butter and milk are heated over a double boiler and mixed, the, off the heat, the flour stirred in, then the five eggs are stirred in. The eggs whites are whisked with the sugar and salt to stiff peaks and the batter folded in. The cake is then baked in a water bath at 150C for 90 minutes.
From the video, it looks like medium eggs (about 50g) were used. If like me you usually buy large eggs then the extra yolk could be as much as 50g. So I'd suggest cutting back on the yolks slightly. The water bath should help cook the base. Also definitely use a metal tin, as in the video: glass or ceramic containers do not conduct the oven's heat to the bottom of the cake so efficiently.

Finally you mention whisking: definitely whisk to stiff peaks for the egg whites. But for the batter, you don't want so much air. Instead the aim is to make a stable emulsion.