1. Combine milk and 1 cup cream in a medium pot. Split vanilla beans in half lengthwise, scrape out seeds and pulp with a paring knife, and add to pot along with empty pods. Bring to a boil over high heat. Remove from heat, cover, and let infuse 30 minutes.
2. Beat egg yolks and sugar with the whisk attachment at high speed until mixture is thick, pale yellow, and falls in ribbons, about 3 minutes. Bring milk and cream back to a boil, then pour into a spouted measuring cup. On low speed, slowly drizzle hot cream into egg mixture, 1/4 cup at a time. When half the cream has been incorporated, you can add the rest more quickly. Strain the mixture and let sit 20 minutes.
3. Preheat oven to 325°. To make your custard especially silky, skim all traces of white foam from cream (it will be quite a lot, about 1 cup).
4. Pour mixture into six small (1/2 cup) coffee cups or ramekins. Place in a roasting pan, then pour hot water into pan to come halfway up outsides of cups. Cover pan with foil and bake about 30 minutes, until custard jiggles only slightly in center. Using a sturdy flat spatula, transfer custards to a rack to cool completely. Cover with plastic wrap; chill at least 4 hours and up to 3 days.
5. Set a bowl over a saucepan filled with 1 in. water (not touching water) and bring to a boil. Add chocolate and cocoa butter (if using oil, melt chocolate first and then stir in oil). Working with 1 pot de crème at a time, and keeping chocolate warm in double boiler, spoon 1 to 2 tsp. chocolate onto custard (depending on size of cup) and tip cup to form a thin, even layer of chocolate. Don't add extra chocolate, even if there's some left over; the layer will be too thick. Chill until ready to serve.
6. Whip remaining 1/3 cup cream. Top each pot de crème with a dollop of whipped cream and a sprinkle of almonds.
*Find cocoa butter, grapeseed oil, and stubby, rich Marcona almonds at Whole Foods Market and other well-stocked grocery stores.