1. Heat oven to 425 degrees F. Halve cooled potatoes lengthwise and scoop out the flesh, leaving a 1/4-inch shell and reserving the potato flesh for later use (see note). Cut each shell lengthwise into 3 strips, and arrange strips on baking sheet. Brush the strips with olive oil, and sprinkle with salt and pepper.
2. Bake about 20-30 minutes, or until strips are crisp and golden-brown. Serve with onion-and-chive sour cream, if desired.
3. When potatoes are halfway done, prepare the beef fillets. Heat heavy-bottomed 12-inch skillet over high heat until very hot, about 3 minutes. Season both sides of beef fillets with seasoning mix and salt. Lay fillets in pan, leaving 1/4-inch space between them.
4. Reduce heat to medium-high, and cook without moving fillets until well- browned, about 4 minutes. Flip steaks and cook 4 minutes more for rare, 5 for medium-rare, and 6 for medium.