Place the potatoes in a medium saucepan, cover with cold water, and bring to a boil. Cook until tender when pierced with a fork, 10 to 15 minutes. Preheat the oven to 375 degrees. Drain the potatoes and place them on a baking sheet. Place the pan in the oven and bake for about 10 minutes to dry the potatoes. Remove the potatoes from the oven and transfer them to a large bowl. Add the cream and, using a potato masher, mash the cream with the potatoes. Add the mustard and chiles and mix well. Set aside. In a small saute pan, heat the olive oil over high heat until very hot. Add the onion and garlic and lightly saute for 2 to 3 minutes. Add the cumin and cook with the onions until fragrant, about 1 minute. Add the onion mixture to the potatoes and mix well. Stir in the butter and season to taste with the salt and pepper. (The dish can be made up to this point and refrigerated in a covered container until ready to serve.) Place mashed potatoes in a 2-quart casserole and bake in the oven until hot, about 30 minutes. Serve warm. Per serving: 249 Calories (kcal); 25g Total Fat; (87% calories from fat); 2g Protein; 6g Carbohydrate; 77mg Cholesterol; 68mg Sodium Food Exchanges: 0 Grain(Starch); 0 Lean Meat; 1 Vegetable; 0 Fruit; 5 Fat; 0 Other Carbohydrates Converted by MM_Buster v2.0n.