Peel and quarter the russet potatoes and put them in a large pot. Cover with cold water and salt the water generously. Bring to a boil and cook about 15 to 20 minutes, until fork-tender. Drain well in a colander, pouring away from you so the steam doesn't catch your face.
Return the potatoes to the pot and mash with the 2 tablespoons butter, sour cream, 1 teaspoon grated nutmeg, dried thyme, salt and pepper until smooth and creamy. Set aside.
Heat a large skillet over medium-high heat and add the ground beef. Wash your hands, and anything that touched the raw beef, with hot soapy water. Cook the beef, breaking it up, about 8 to 10 minutes, until browned with no pink left. Check it with an instant-read thermometer: it needs 160°F (71°C). Carefully spoon off any extra fat into a heatproof container. Let the fat cool, then put it in the trash. Never pour it down the drain.
Add the garlic, onion, carrots, green beans and bell pepper. Sauté about 5 to 7 minutes, until the vegetables soften. Stir in the oregano and beef flavour powder. Pour in the red wine (or beef broth) and scrape up the browned bits from the bottom of the pan. Toss in the raisins. Simmer about 10 minutes, until the liquid reduces into a rich, glossy sauce. Season with salt and pepper to taste.
Preheat your oven to 375°F (190°C). Spread the beef filling in an even layer in a glass oven-safe square dish (8-inch square, 2 quart). Set it on a baking sheet to catch any drips. Spoon or pipe the mashed potatoes generously over the top. Scatter a few thin slices of butter over the potatoes and grate a little extra nutmeg over the surface. Bake about 25 to 30 minutes, until the filling is bubbling at the edges and the potato top is golden and crisp. The centre should reach 165°F (74°C).
Set the hot dish on a dry trivet or wire rack and let it rest about 10 minutes, so the filling settles before you scoop it.