*Short-cut: Feel free to use store-bought dulce de leche.
*Stiff dulce de leche problem: If your dulce de leche is cold and a bit stiff, it'll have trouble swirling, to combat this issue simply warm it up in the microwave or in a small saucepan until warm.
*To Make Ahead: You can make this up to two days ahead. To do so, make the entire recipe and transfer to the fridge to chill for up to a day. If it's more than a day, I'd suggest slicing it up and storing it in an airtight container.