Pale, sweet, arguably boring white chocolate is made of three ingredients with a lot of potential -- sugar, milk, and fat (in the form of cocoa butter). When you heat them, they turn to caramel. Some call the result the "Toffee of Milk". The cocoa butter amount matters -- the higher it is, the more willingly melty it gets. Recipe adapted from L'Ecole du Grand Chocolat Valrhona. —Genius Recipes
Heat oven to 266°F (130°C). If the white chocolate isn't already in small chunks or fêves, chop it coarsely. Scatter it on a clean, dry rimmed baking sheet.
Roast chocolate in the oven for about 45 minutes, stirring and smearing the chocolate around with a spatula every 5 to 10 minutes (make sure the spatula is clean and dry when you start). Don't worry if it looks lumpy and crumbly at times -- it will smooth out as you stir.
Continue cooking until the chocolate is as dark as you like (we like a rich toffee color). Stir in sea salt to taste.
Pour into a jar to store -- it will harden as it cools, and may look mottled (this is normal for untempered chocolate). Store at room temperature, and warm it in a pot of barely simmering water when you're ready to use it. It should keep for several months.
Alternately: If you keep roasting until it seizes into crumbles, don't worry. It is completely salvageable and, in fact, it may be a handier form to keep around for baking. That way, you can freely toss handfuls into cookies or scones, brownies or banana bread. You can also force it to become completely smooth with the aid of a blender or a fine mesh strainer if you wish -- just warm with a little cream or neutral oil in a double boiler, then either blend or strain.