Heat 1 tsp olive oil in a non-stick 10-inch skillet over medium-high heat. Once hot, add garlic and spinach and saute until spinach begins to wilt, about 30 seconds. Remove from heat, stir in basil and set aside. To assemble sandwich, spread Mozzarella and Feta cheese over one slice of bread into an even layer. Layer tomatoes in a single layer over cheese. Spread spinach mixture over tomatoes then sprinkle olives and red onions over tomatoes. Season with freshly ground black pepper and top with remaining slice of bread.: As the oil warms you should notice a faint shimmer on its surface and a gentle aroma that hints at fruitiness. This quick rise in temperature prepares the skillet so the garlic sizzles immediately when it hits the pan, releasing its fragrance without burning. Use a non-stick 10 inch skillet to keep the spinach from sticking and to promote even cooking. A common mistake is overheating the oil so the garlic smokes, producing bitterness; keep the heat steady and reduce it if the oil begins to smoke.
Spread 1 tsp olive oil evenly over skillet, add sandwich and heat over medium-low heat. Cook until bottom is golden brown, about 3 - 4 minutes, then remove sandwich from pan. Spread remaining 1 tsp olive oil evenly along skillet, carefully rotate sandwich to opposite side and return to pan over medium-low heat. Cover skillet with lid and cook until bottom is golden brown, about 2 - 3 minutes. Serve immediately.: You will hear a delicate sizzle and see the spinach quickly collapse into glossy, darker green ribbons. The brief saute concentrates the green flavors while evaporating excess moisture, which prevents the sandwich from becoming soggy. Stir constantly for even wilting and pull the pan off the heat the moment the leaves lose their raw stiffness. Overcooking will turn the spinach wet and limp which dulls the texture.
Recipe Source: Cooking Classy: Off the heat the residual warmth will gently release the herbal oils from the basil , keeping the aroma vibrant. Stirring now helps the herb integrate without wilting it into oblivion. Setting the mixture aside lets it cool slightly so it does not melt the cheeses prematurely when assembled. A common slip is adding the basil too early so it loses its fragrance.
To assemble sandwich, spread Mozzarella and Feta cheese over one slice of bread into an even layer: The cheeses should be distributed so that melting is even, creating a cohesive interior. Shredded Mozzarella cheese should form a continuous layer while crumbled Feta cheese dots the surface with pockets of tang. Using an even layer helps avoid cheese clumps that either fail to melt or leak out. Pressing too hard while assembling can flatten the bread and change the texture.
Layer tomatoes in a single layer over cheese: Arrange the tomato slices so they lie flat, covering the cheese but not overlapping excessively. The warmth from the bread and cheese will soften the tomato slightly, releasing sweet, savory juices that marry with the melting Mozzarella cheese . If your tomato is overly juicy blot it with a paper towel to prevent soggy bread . Too many overlapping slices can create a cold center and uneven melting.
Spread spinach mixture over tomatoes then sprinkle olives and red onions over tomatoes: The warm spinach melds into the layers, adding a tender texture, while diced black olives and chopped red onion provide briny and sharp contrasts. Scatter them for even flavor distribution. Avoid piling too much spinach in one spot, which can cause uneven warmth and texture.
Season with freshly ground black pepper and top with remaining slice of bread: A few twists of black pepper wake up the components and unite the flavors. Cap the sandwich gently so the layers stay in place, but do not compress too firmly. Pressing excessively will force juices out and make the bread soggy, while too light a touch can allow fillings to fall out during cooking.
Spread 1 tsp olive oil evenly over skillet, add sandwich and heat over medium-low heat: The first sear is where the bread develops golden color and crispness. You should hear a steady, low sizzle as the oil meets the bread, and the pan should be warm enough to toast without burning. Medium low heat ensures the interior cheeses have time to melt. A common error is using high heat which crisps the outside too quickly and leaves cheese unmelted.
Cook until bottom is golden brown, about 3 to 4 minutes, then remove sandwich from pan: Watch for a deep golden color and a firm crust under the sandwich, you can gently lift a corner to check. That sound of a crisp crust forming is a cue that it is ready to flip. If you find the outside browning before the inside melts, lower the heat and give the cheese more time to soften. Flipping too early can tear the bread.
Spread remaining 1 tsp olive oil evenly along skillet, carefully rotate sandwich to opposite side and return to pan over medium-low heat: Adding the remaining oil readies the pan for the second side, ensuring even browning and avoiding sticking. Rotate the sandwich so the untoasted side meets the warm surface, and maintain medium low heat for gradual melting. Be mindful when rotating to avoid spills; a spatula and gentle lift help preserve the sandwich shape.
Cover skillet with lid and cook until bottom is golden brown, about 2 to 3 minutes: Covering helps trap heat so the cheeses become perfectly gooey while the second side crisps. You should see faint steam and hear a quieter sizzle as trapped heat completes the melt. Remove the lid when the crust is golden and slightly firm to the touch. Leaving it covered too long can over soften the bread and reduce crispness.
Serve immediately: The ideal bite is right away, when the exterior is crisp and the interior is hot and melty. Serve on a plate and slice if you like, noticing the stringy Mozzarella cheese and the pockets of briny Feta cheese . Letting the sandwich sit too long will cool the cheese and soften the crust, losing the contrast that makes the sandwich special.