This is like a hand-held quiche, perfect for parties.
Frozen spinach holds a high volume of intracellular water that raw vegetable weights fail to convey. Squeeze the thawed greens through a fine-mesh strainer or clean kitchen towel until completely dry. Excess moisture creates steam inside the dough layers, preventing the butter in the puff pastry from rendering properly and leaving the interior soggy. Working with cold pastry is critical; if the fat within the dough melts before hitting the oven heat, the characteristic flaky layers will fail to form.
Dietary adjustments require careful substitution ratios to maintain structural integrity. Swap butter for neutral vegetable oil in equal measure during the initial onion sauté without altering the final texture. Plant-based milk substitutes work identically in the egg wash, provided they contain enough protein to brown properly under heat. Firm sheep-milk feta can be replaced with salted firm tofu mixed with a pinch of nutritional yeast for a dairy-free alternative that retains the necessary sodium content. Assemble the unbaked triangles and freeze them on a parchment-lined tray for two hours before transferring them to a sealed container. Bake them directly from frozen by extending the standard 180C oven time by five to seven minutes.