In a large saucepan, melt 1 tablespoon of the butter over medium heat. Add the onions and cook, stirring occasionally, until softened.
Mix in the garlic and cook until just fragrant, 30 seconds to 1 minute. Add the chicken pieces and cook, stirring occasionally, until all the sides are golden.
Pour in the white wine, scrapping any bits from the bottom of the pan, and add the chicken broth and mushrooms. Bring to a boil.
Reduce heat to a simmer and add the bay leaves, thyme, mustard, curry powder, Worcestershire sauce, and salt and pepper to taste Cover and cook for 25 minutes, stirring occasionally. Discard the bay leaves.
In a small pan, melt the remaining 4 tablespoons butter over medium heat. Whisk in the flour to create a paste.
Slowly whisk in 1/2 cup (120 milliliters) of the simmered broth until incorporated. Repeat with about 2 more cups (470 milliliters). Pour the mixture back into the pot with the chicken and stir to combine thoroughly.
Cook until just thickened. Season as needed with salt and pepper, then stir in the cream.
Divide among the puff pastry shells and top with parsley. Serve the Pasteitje met Ragout immediately.