Clean and slice the leeks. Peel and chop the potatoes.
Whisk together the wine, melted butter, Worcestershire sauce, Herbs de Provence, salt and pepper.
In the liner of a slow cooker, layer the leeks, potatoes and sirloin steaks.
Pour the wine mixture evenly over the top.
Cook until the steak can easily be shredded with a fork, 6 - 8 hours on LOW heat.
Shred the steak with two forks.
Stir in the frozen spinach and Boursin cheese.
Continue to cook on low heat until the Boursin has completely melted and combined with the steak, potatoes, leeks and spinach.
Allow the filling to cool.
The steak pie filling can be stored in an air-tight container in the refrigerator for up to three days.
When ready to serve, preheat the oven to 400 degrees F.
Allow the puff pastry to thaw according to package directions.
Invert your ramekin baking dishes on top of the puff pastry. Use a sharp pairing knife to cut circles of pastry to fit the tops of your dishes. Cut a small "x" into the center of each circle.
Fill each dish to the top with prepared steak pie filling. Place a circle of puff pastry on top of each dish. Pressing down lightly.
Place the dishes into the hot oven. Bake until the puff pastry is golden brown and cooked through, 20 - 25 minutes.