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Preheat oven to 350 degrees. Make dough: In a food processor, pulse almonds until finely ground. Add sugar, flour, zest (if desired), and salt; pulse until combined. Add butter, pulsing until coarse crumbs form with no large butter lumps (dough should clump together when squeezed with fingers).
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Immediately transfer dough to a 9-inch tart pan with a removable bottom. Using a measuring cup, evenly press dough in bottom and up sides of pan.
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Bake in center of oven until golden brown and firm to the touch, about 20 minutes. Transfer to a wire rack to cool completely, about 1 hour.
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Make ganache: Place chocolate in a large mixing bowl. In a small saucepan, bring cream to a boil. Pour hot cream, through a sieve, over chocolate. Stir until smooth and creamy in texture. Mix in vanilla.
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Pour chocolate mixture into center of cooled tart shell (if chocolate is lumpy, pass through a sieve). Let stand until set, about 2 hours, or chill for 1 hour.