Who said "You are beginning to understand."?

This quote is attributed to Palpatine.

You are beginning to understand. - Palpatine

"You are beginning to understand."

Palpatine

"Did you ever hear the tragedy of Darth Plagueis the Wise?"

"The dark side of the Force is a pathway to many abilities some consider to be unnatural."

"Have you ever heard of the tragedy of Darth Plagueis? I thought not."

"Unlimited power!"