Preheat oven to 375°F. Lay out your puff pastry on a parchment-lined baking sheet. Poke several holes in the pastry using a fork and set aside. While the oven heats, roughly chop your greens, then wash and dry them thoroughly. Next, thinly slice 4 garlic cloves.
Heat a pan on medium-low heat. Add 1/4 cup olive oil and garlic slices. Cook until the garlic is light golden brown, about 3 minutes. When your kitchen smells of delicious garlic, add your chopped and cleaned greens. Season generously with salt and cook until dark green and reduced in volume by about 1/2. Because this recipe allows you to use any green tops, it's essential to taste as you go—it might need more salt, a little lemon or vinegar, even a dash of honey.
When the greens are tasting great, transfer to a medium bowl. Using a mandolin, thinly slice 1 medium potato into the bowl, then cover with 150g goat cheese and toss to mix. Use your hands to separate the potato slices because they will want to stick together.
Transfer the contents of the bowl to the centre of your puff pastry, and smooth it out into an even layer, leaving 1-2 inches around the edges. Fold the border pieces towards the middle, crimping the corners together as you go to create a seal. If the corners are looking long, trim any excess using scissors.
Using a pastry brush, or your hands, coat the folded pastry edges with 2 tbsp heavy cream, or 1 egg whisked. Garnish with sesame seeds, if you have them. Bake for 40 minutes, or until golden brown. Serve warm and enjoy!
