Heat oven to 350. Grease 10 inch springform pan and line with greased parchment (not waxed paper). Line a cookie sheet with greased parchment. Whisk together eggs and vanilla. Remove as much skin from the hazelnuts as you can and process them with one cup of the powdered sugar for 30 seconds. Add both sugars and process briefly to combine. With processor running, pour in egg mixture and process for 15 seconds or until smooth. Reserve ½ to 1/3 cup of the batter. Pour remaining batter into the springform pan and smooth with spatula. Pour reserved batter onto the cookie sheet and spread out into a 7-8 inch disk.
Bake crust 25-30 minutes; disk 20-25 minutes. Cool on a wire rack. Chop up the disk into 1/8 inch pieces and soak in ¼ cup Amaretto (but do not soak for more than 15 minutes).
Amaretto cheesecake filling:
Sprinkle gelatin over ¼ cup Amaretto, let stand 5 min. Heat in sauce pan with hot (not boiling) water stirring for 4 min. Leave in hot water to stay warm. Beat cream cheese with mixer for 1 minute. Add lemon juice and zest. Beat cream to soft peaks. Fold 1/3 cream into cream cheese. Fold in remaining whipped cream and soaked macaroon bits.
Pour into prepared pan, cover with plastic wrap. Refrigerate at least 3 hours or preferably overnight.