Encrusted silver fake Lego, that is, as the Sterling Silver Building Blocks being offered by the custom build department of Tiffany & Co. don't appear to be officially licensed or come with instructions, plus they're described as "numbered and lettered building blocks," and not Lego or even the US bastardisation "Legos".
You do get 10 pieces of generic building brick toy for your money, though, with most featuring a sterling silver top placed on an American walnut base, with one large 5x2 piece that's entirely silver. There's not much you can make with 10 Lego-style bricks, mind, so you might need to buy 20 sets if you're super rich and planning to build a bespoke shimmery castle for your beloved this Christmas.
They can be engraved too, but that's an extra $25. Which really pushes it out of the present budget range. [Tiffany & Co.]