Heat butter, water, salt,sugar in the sauce pan over medium heat until butter is completelt melted and mixture start simmering.

Add cake and bread flour, stir mixture well until it does not stick to the pan.

Add beaten egg portionwise, mix until incorporate and see the ribbon like mixture.

Transfer mixture to pipping bag. Pipe on parchment paper in totoro shape

Bake at 190 C for 20 minute and 150 C for 15-20 minute. let the dough cool down in the oven with the dorr left slightly opened.

Prepare chocolate filling by heating milk and chocolate in a pot under low heat. Stir until smooth, then add corn flour, mix well and heat until mixture become thicken. Cool down completely before piping the filling into the choux.