Chocolati
If you're looking for a dedicated hot chocolate authority, Chocolati is it. They specialize in artisan chocolate, and their unparalleled cocoa is rich and creamy and comes in a variety of flavors, from peanut butter to salted caramel to Aztec. The "Dark Vader" (raspberry and dark chocolate) is an especially popular menu item. (If you're looking for a caffeinated alternative, I was also tickled to see a special called "Bella Where The Hell Have You Been, Mocha?" on the menu on a recent visit to the Greenwood location, featuring a salted blood orange mocha with a bittersweet chocolate truffle.)
Various locations

Le Pichet Like List
Is the description hot cocoa "as thick and rich as melted chocolate bars" from The Polar Express is also a core childhood memory for you? (For the record, I grew up with the Chris Van Allsburg picture book, not the 2004 CGI uncanny valley monstrosity starring Tom Hanks.) If so, you can make the dreams of your youth come true with the swoon-worthy Parisian-style chocolat chaud at the enduring French bistro Le Pichet. Owner Jim Drohman brought his dessert-worthy recipe stateside after working a brief stage for a famous French chocolatier. It's made to order and topped with a luxurious dollop of whipped cream. 
Pike Place Market

Maíz Like List
If you can summon the courage to brave the throngs of tourists congesting the streets of Pike Place, you'll be rewarded with some true hidden gems. This colorful, pint-sized tortillería tucked away in the market is one of my favorite places to visit when I find myself in the area. Their champurrado, a chocolate-flavored version of the corn-based beverage atole, is thickened with fresh masa harina, resulting in a silky, comforting drink that warms you from the inside out. The Mexican mocha is also exquisite.
Pike Place Market

Rey Amargo Chocolate Shop Like List
This Capitol Hill cafe, started by a chocolate company based in Jalisco, Mexico, serves a dizzying array of high-quality drinking chocolates, including classic hot chocolate, iced drinks and frappes, Aztec- and Mayan-inspired versions, and French, Spanish, and Swiss hot chocolate. The South American variety contains melty chunks of Monterey Jack cheese for a traditional Colombian salty-sweet combo—it may sound unusual, but don't knock it till you try it. Whatever you order, be sure to order a churro for dipping for optimal bliss.
Capitol Hill