Prep the Crust Shells: Preheat your oven to 190°C / 375°F. Lightly grease a standard 12-cup muffin tin with the melted butter. Roll out your thawed pastry dough onto a lightly floured surface. Cut pastry rounds using a 3.5-inch circular cookie cutter or a wide drinking glass rim. Press each circle gently into the muffin tin cavities, ensuring the dough fits snugly against the bottom and sides. Use a fork to prick the bottom of each shell a few times to prevent bubbling.
Sauté the Spinach: Heat olive oil in a small skillet over medium heat. Sauté the minced garlic for about 30 seconds until fragrant. Add the chopped spinach and cook for 2–3 minutes until completely wilted. Remove from heat and press the spinach firmly into a fine-mesh strainer or squeeze inside a clean kitchen towel to remove all excess moisture. This is a crucial step to prevent a soggy pastry base!
Mix the Egg Custard: In a medium mixing bowl, whisk together the eggs, whole milk or cream, sea salt, black pepper, and dried herbs until smooth and fully combined.
Assemble and Bake: Divide the squeezed, wilted spinach and most of the crumbled feta evenly among the bottoms of the raw pastry cases. Slowly ladle the egg custard mixture into each cup, filling them about 3/4 of the way to the top. Do not overfill. Top off each tartlet with a few pieces of chopped sun-dried tomatoes and the remaining bits of feta cheese, exactly as styled in image. Bake for 20–25 minutes until the pastry edges turn a crisp golden brown and the egg centers are set.
Cool and Serve: Let the mini quiches cool inside the tin for about 5 minutes. Gently run a thin knife around the edges to lift them out. Serve warm or at room temperature!