Heat 1 tablespoon of the grapeseed oil over medium heat in a large saute pan and add 1 tablespoon of the butter (reserving the other 2 tablespoons oil and the other 3 tablespoons butter). Reduce the heat to low and slowly cook the leeks until tender. Transfer to a utility platter, cover and keep warm. (Keep the same pan handy to sear the scallops.)
While the leeks are cooking, in a separate medium saucepot heat 1 tablespoon of oil over medium heat (reserving the last tablespoon of oil) and saute the onion and garlic until the onion becomes translucent. Add the mango peach juice and curry paste and let reduce by two-thirds. Whisk in the chocolate chips and cook for about 10 minutes to integrate flavors.
While the sauce is cooking, dust the scallops on both sides with chili powder and cocoa powder, and season with a little salt.
Return to the saucepot, and reduce the heat to low. Take 1/4 cup of the hot sauce and put it into a separate bowl. Gradually add the sour cream into the hot sauce, a spoonful at a time to temper the sour cream and keep it from "breaking."
Gradually add the bowl of tempered sour cream to the sauce a little at a time and allow to thicken over low heat, about 5 more minutes.
While the sauce is thickening, return to the pan in which you sauteed the leeks and if you have not already done so, remove them to a utility platter to keep warm. Wipe out the same pan, heat the remaining 1 tablespoon oil over medium-high heat to the smoking point and melt 1 tablespoon of the butter in it (reserving the last 2 tablespoons of butter). Sear each side of the scallop leaving undisturbed for the first 2 minutes or so to let the caramelization process to begin. This will not only allow the seasonings integrate into the surface of the scallops, but will prevent tearing. Further cook the scallops until you see (from the side) that they are beginning to turn opaque inside. When you notice that the opacity extends about 1/4 of the way down from each flat side of the scallop, remove the scallops to a plate and cover them with a pot lid to allow carryover cooking to take over, to avoid overcooking the scallops.
Spoon some leeks into the center of serving plate. Top with scallops and spoon curry sauce around.