Place a mixture of oil and butter in the bottom of a skillet or sauté pan. Add the spinach and garlic, and cook for about 15 minutes.
When it's done cooking, remove it from the heat, add the crème fraîche, and give it a stir.
Roll out the puff pastry on a baking mat and try to shape it into a rough square. Then cut the dough into 4 squares using a knife or a serrated pastry wheel.
Preheat the oven to 180°C. Place one to two tbsp of spinach on each square, followed by pine nuts (optional) and one or two slices of goat cheese.
Gently seal the pastry by pressing lightly along the edges and corners. Repeat this step for the remaining pastries.
Repeat the process for the remaining pastries, then brush them with egg yolk using a pastry brush. Place a baking rack under the baking mat, and bake for 15 minutes.
Enjoy these spinach puff pastries while they're still hot, served with a green salad.