Such a 1:1 transformer is not the best part to provide the amount of power and efficiency for step up like you need for instance for automotive ballasts etc ;-)
Even this non ordered winding inside the core I regard as a problem for high voltage applications for possible weak points for break down.
The Coilcraft part has inside the data sheet a rated winding to winding isolation of 500 V , oh that part must be very good for making 500Volts some fool may guess
For my ballasts I am using the PCB itself as the transformer with 2 loops on the primary and few more on the secondary with a planar ferrite to have a minimum of capacitance and very little ohms as well.