Preheat the oven to 250°. In a medium saucepan, add the butter, granulated sugar, brown sugar, cocoa powder and cream. Place the pan over medium heat and whisk constantly until the mixture begins to simmer around the edges, the butter melts and the sugars dissolve. Remove the pan from the heat.
In a medium bowl, add the eggs and whisk in ½ cup of the hot cocoa mixture. Whisk until smooth, then return the egg-cocoa mixture to the saucepan, whisking to combine. Pour the custard into a 9-inch square baking dish (the custard should come at least ¼ inch up the sides of the pan) and bake for 8 minutes. Rotate the pan and bake until the edges of the custard are just set and the center jiggles slightly, about 10 minutes more.
Fill a large bowl with ice and water. Set a fine-mesh sieve over a medium metal bowl and strain the hot custard through the sieve, using a rubber spatula to push the custard through the sieve and into the bowl. Place the bowl in the prepared ice-water bath and whisk the custard constantly for 30 seconds. Keep the custard over the ice bath and cool, stirring occasionally, until the custard is completely cooled, about 15 minutes. Transfer the custard to an airtight container and refrigerate for at least 3 hours. (The custard can be refrigerated for up to 4 days.) 4. Divide the custard among 6 small bowls. Drizzle with olive oil, sprinkle with sea salt and serve.