Thaw phyllo pastry and separate sheets according to package directions. Keep pastry not being used covered with clean damp dish towel to keep it from drying out. Place half of pastry sheets in a greased 15x10x1-inch baking pan, one by one, brushing each sheet quickly and all over with melted butter.
Combine nuts, 1/2 cup sugar, and cinnamon; sprinkle over buttered pastry. Place remaining sheets on top, brushing each with melted butter. Cut baklava pastry into 2-inch diamonds. Bake at 400° until brown and crisp, about 30 to 35 minutes. Meanwhile, in a saucepan, combine remaining 3/4 cup sugar, honey, 1 cup water, and lemon juice; bring to a boil. Boil baklava syrup for about 20 minutes, stirring occasionally, until syrupy. Cool and pour over baklava.