Place the 12 ounces of finely chopped white chocolate in a medium heat-proof bowl. Ensure the pieces are uniform in size to promote even melting.
In a small saucepan over medium heat, bring the heavy cream just to a simmer. Watch closely; you want small bubbles to form around the edges, but do not let it come to a rolling boil.
Pour the hot cream over the chopped white chocolate. Let it sit undisturbed for 3 minutes to allow the heat to penetrate the chocolate.
Using a rubber spatula, gently stir the mixture starting from the center in small circles. Continue until the chocolate is completely melted and the ganache is glossy and smooth.
Stir in the limoncello, lemon zest, and salt until fully incorporated. If you prefer a completely smooth texture, you may strain the zest out at this stage, though keeping it adds a pleasant aromatic texture.
Cover the bowl with plastic wrap, pressing it directly against the surface of the ganache to prevent a skin from forming. Refrigerate for at least 2 hours, or until the mixture is firm enough to scoop.
Once firm, use a melon baller or two teaspoons to scoop small portions of the ganache. Roll them quickly between your palms to form spheres and place them on the parchment-lined baking sheet.
Return the rolled truffles to the refrigerator for 30 minutes to firm up again before the final coating.
Melt the remaining 4 ounces of white chocolate in a double boiler or in 20-second bursts in the microwave.
Use a fork to dip each chilled truffle into the melted chocolate, shaking off any excess. Place them back on the parchment paper to set completely.