For custard:
Place yolk, milk, sugar, cornstarch and salt in blender. Blend 30 secs to 1 minute.
Microwave on high up to 1 minute stirring every 10 seconds till thickened.
Whisk in butter and vanilla. Cool.

For chocolate icing:
Place oil and chips over double boiler until melted, stir to combine. Pour on plate when ready to ice.

For pate choux:

Preheat oven to 375.
Bring water, butter, salt and sugar to boil.
Dump in flour, stir to paste and continue over heat until it starts to stick to bottom of pan.
Cool slightly.
Dump in mixer and beat in eggs one at a time.
Whip to thin batter.

Pipe or shape on parchment to 8 - 4 inch tubes.
Increase oven to 425, bake for 15 minutes.
Reduce to 350 and bake another 10.
Pierce end to let steam escape. Cool.

Fill with custard and dip in chocolate.