1. Preheat the oven to 180 °C (350 °F).
2. Sauté the beef over high heat in a drizzle of oil, then add the Basque vegetables (frozen).
3. In a bowl, mix the spice mix with the cooking sauce and 300 ml (1 1/4 cups) of hot water. Divide the mixture in half, add the sour cream to one half, and set it aside.
4. Pour half of the marinade over the beef, add half of the grated cheese, and mix well. Heat for 1 minute.
5. Heat the tortillas:
- in the microwave: pierce the bag and place it in the microwave. Heat for 35 seconds at full power (800 watts). Open the bag and prepare the tortillas.
- in the oven: remove the tortillas from the bag, separate them, and wrap them in aluminum foil or parchment paper. Heat for 10 minutes. Keep them covered until ready to serve.
6. Fill each warm tortilla with a little bit of the filling, roll them up, and place them folded side down in a greased dish with a knob of butter.
7. Pour the remaining filling (with sour cream) over the tortillas and sprinkle with grated cheese.
8. Bake in the oven for 10 minutes until they are nicely browned.