Line a plate with kitchen roll; place a layer of 2 or 3 slices of aubergine onto the kitchen roll. Sprinkle aubergine with sea salt. Repeat layers of aubergine sprinkled with salt until all aubergine slices are stacked. Place 2 pieces of kitchen roll onto the stack and place a plate on top of the kitchen roll. Lay a heavy book or tins of food onto the plate to squeeze out moisture. Allow to drip for 20 minutes to 2 hours. Rinse and pat dry.
Beat eggs with milk in a shallow bowl. Place breadcrumbs into a separate bowl. Dip aubergine slices in the egg mixture and gently press into the breadcrumbs to coat; set aside.
Preheat oven to 180 C / Gas 4. Grease a square baking dish.
Heat olive oil in a large pan over medium-high heat; fry aubergine slices in the hot oil in small batches until golden brown, about 1 to 2 minutes per side. Drain on kitchen roll.
Pour about 60ml of tomato passata into the bottom of the prepared baking dish and arrange a layer of aubergine slices to cover the sauce. Scatter basil and a few slices of smoked mozzarella cheese over aubergine; repeat layers, ending with a layer of sauce on top. Sprinkle Parmesan cheese over the top.
Bake in the preheated oven until heated through and the cheese has melted, about 15 minutes. Serve immediately.
Let aubergine slices drain for at least 20 minutes; you can leave them for up to 2 hours. You will get a crispier aubergine slice when fried, not a soggy one.