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1
Cook garlic in butter in a 3-quart heavy saucepan over moderately low heat, stirring, 1 minute.
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2
Add flour and cook roux, whisking, 3 minutes.
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3
Add milk in a stream, whisking.
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4
Add bay leaf and bring to a boil over moderately high heat, whisking constantly, then reduce heat and simmer, whisking occasionally, until liquid is reduced to about 4 cups, about 10 minutes.
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5
Whisk in salt and white pepper, then remove from heat and discard bay leaf.
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6
Cover surface of sauce with wax paper until ready to use.
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7
Coarsely chop 1/3 cup hazelnuts and reserve for sprinkling over lasagne.
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8
Puree parsley, Parmigiano-Reggiano, 2/3 cup oil, garlic, 1 teaspoon salt, 1 teaspoon pepper, and remaining cup hazelnuts in a food processor until pesto is smooth, about 1 minute.
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9
Whisk egg in a bowl, then stir in ricotta, 1 cup parsley pesto, remaining teaspoon salt, and remaining 1/4 teaspoon pepper until combined well.
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10
Stir together 1/4 cup pesto and remaining 1/4 cup oil in a small bowl for drizzling over lasagne.
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11
Put oven racks in upper and lower thirds of oven and preheat oven to 450F.
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12
Oil 2 large baking sheets.
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13
Brush eggplant with oil on both sides, then arrange in 1 layer on baking sheets and sprinkle with salt and pepper.
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14
Bake eggplant, switching position of sheets halfway through baking and turning slices over once, until tender, 20 to 25 minutes total.
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15
Put oven rack in middle position and reduce oven temperature to 425F.
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16
Lightly oil a 13- by 9- by 2-inch glass or ceramic baking dish (3 quart) and line a larger shallow baking pan with foil.
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17
Spread 1 cup bechamel in baking dish and cover with 3 pasta sheets, leaving spaces between sheets.
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18
Drop 1 cup ricotta mixture by spoonfuls over pasta, spreading evenly (layer will be thin), then top with 1 layer of eggplant, cutting rounds to fit if necessary.
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19
Make 1 more layer each of bechamel, pasta, ricotta, and eggplant.
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20
Spread with 1 cup bechamel and cover with remaining 3 pasta sheets.
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21
Spread remaining cup ricotta mixture over pasta, then spread ricotta with remaining cup bechamel and top with remaining eggplant in 1 layer (you may have a few slices left over).
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22
Sprinkle Parmigiano-Reggiano over eggplant and scatter with reserved chopped hazelnuts.
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23
Tightly cover baking dish with oiled foil (oiled side down), then set dish in foil-lined pan (to catch drips) and bake lasagne 30 minutes.
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24
Remove foil and bake until golden and bubbling, 10 to 15 minutes more.
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25
Let lasagne stand 15 to 20 minutes before serving.
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26
Serve lasagne drizzled with pesto.
