Begin heating it and stirring constantly until it's completely melted. Then pour half of it into the prepared pan.
For the pralines layer, get your second saucepan and pour in the brown sugar, whipping cream, butter & 1 teaspoon of vanilla. Bring to a boil over medium heat, stirring constantly. Boil for about 1 minute, then remove it from the heat. Immediately whisk in the powdered sugar, then gently stir in the pecans.
Allow the mixture to thicken and cool slightly then pour most of it over the fudge. I reserve a little to pour on top! It will slightly set up but you don't have to wait for it to completely harden; then pour on the remaining fudge and the remaining praline mixture. If your fudge has hardened, you can put it back on the stove for a minute and stir it gently to reheat and soften (be careful not to scorch it!). I swirled white chocolate fudge and pralines together a bit so it would be pretty!
Allow it to set up for at least 4-6 hours at room temp or at least 2 hours in the refrigerator. When it's set, you can use a knife to slide around the edges (especially if the fudge touches the pan anywhere), then lift out the parchment and fudge and cut it into squares!