For the love of puff pastry {Alsatian Leek & Swiss Chard Tart}

Name: For the love of puff pastry {Alsatian Leek & Swiss Chard Tart}
Cuisine: European, French, Mediterranean
Ingredients: 1 sheet frozen puff pastry (half of the 17.3 oz package), thawed; 2 Tbsp butter; 2-3 large leeks ( white and pale green parts only) coarsely chopped and washed well.; 1 bunch Swiss Chard, ribs removed & cut up, leaves chopped (about 2.5 cups); 1 1/4 C whipping cream; 3 large eggs; 2 large egg yolks; 1 Tsp salt; 1/4 Tsp ground black pepper; pinch of ground nutmeg