To make the crust:
Preheat oven to 350°F.
Finely grind graham crackers in processor. Mix in sugar. Add butter; mix to blend.
Press onto bottom and up sides of 10-inch-diameter glass pie dish. Bake until light brown around edges, about 12 minutes. Cool completely.
To make filling:
Whisk all ingredients except the ice cream in medium bowl. Coarsely chop almonds and set aside.
Slightly soften ice cream in microwave in 10-second intervals. Measure 1 cup ice cream; cover and freeze for another use. Spoon remaining ice cream into large bowl.
Working quickly, add pumpkin mixture and almonds and fold just until swirled into ice cream. (Do not blend completely.)
If ice cream begins to melt, freeze until almost firm.
Spoon ice cream filling into cooled crust, cover with plastic, and freeze until firm, at least 6 hours.
Top with whipped cream, if desired.
To do ahead: Can be made 2 days ahead and kept frozen.