In a large bowl, whisk together 150 g all-purpose flour, 0.5 tsp baking powder, and 0.25 tsp salt. In another bowl, combine 450 ml dashi stock, 2 beaten eggs, and 1 tsp soy sauce. Pour the wet mixture into the dry ingredients and whisk until just smooth; a few small lumps are fine. The batter should be thin, like crepe batter. Let it rest while you prepare the fillings.