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1
Coarsely chop nuts.
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2
Pour 3/4 cup sugar into a 10- to 12-inch nonstick frying pan. Shake pan often over high heat until sugar melts and turns golden, 5 to 8 minutes; watch carefully. At once, stir in nuts, then immediately pour onto a 12- to 14-inch sheet of foil. With a spoon, press mixture to flatten slightly. Let cool, then break brittle into about 1/4- to 1/2-inch chunks. If making ahead, store airtight up to 3 days.
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3
In a 10-inch cheesecake pan with removable rim at least 2 1/2 inches tall, mix cracker crumbs, 1/4 cup sugar, cinnamon, and butter. Press crumb mixture evenly over the bottom and 1 1/2 to 2 inches up sides of pan.
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4
In a bowl, beat cream cheese and eggs with a mixer until smooth. Add 3/4 cup sugar, lemon peel and juice, lime peel and juice, vanilla, and 1/4 cup liqueur; beat until smooth. Stir in 1 1/2 cups of the nut brittle. Pour into crust-lined pan.
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5
Bake in a 325u00b0 oven until center barely jiggles when cake is gently shaken, about 1 hour.
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6
Meanwhile, mix sour cream with 1/4 cup sugar and 1 tablespoon liqueur. Spoon onto hot cheesecake and gently spread to cover top. Return to oven and bake until sour cream is set when gently shaken, 10 to 15 minutes longer.
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7
Run a thin-bladed knife between cake and pan rim. Refrigerate cake until cool, at least 3 hours. Serve, or cover and chill up to 2 days.
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8
Remove pan rim, sprinkle remaining nut brittle onto cake, and cut cake into wedges.
