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1
Preheat the oven to 350 degrees F. In a medium bowl, combine the flour, 3 tablespoons sugar and a pinch of salt.
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2
Add the butter and lemon zest and work into the flour mixture until crumbly using your fingers or a pastry cutter.
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3
Separate the whole egg, adding the white to the other two for the meringue topping.
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4
Add the yolk to the dough and mix in until a soft dough forms.
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5
Press into the bottom and up the sides of a 9-inch pie plate.
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6
Bake until golden, about 25 minutes.
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7
Cool.
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8
Lightly score the pie shell with a sharp knife (cutting about halfway through the crust) into 10 slices to make cutting the frozen pie easier.
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9
Place the lemon ice cream in a large bowl and mix with a stiff spatula or wooden spoon until smooth, about 2 minutes.
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10
Mix in the food coloring if using.
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11
Spoon into the pie shell, smooth the top and place in the freezer until firm, 2 hours or overnight.
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12
Preheat the oven to 500 degrees F. Place all 3 egg whites, the remaining 1/3 cup sugar and a pinch of salt in a large heatproof bowl and put it over a pot with 1-inch of simmering water.
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13
Whisk until the sugar is dissolved, the eggs are warm and the mixture is fluffy.
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14
Whip with an electric mixer on medium-high speed until cooled, thick, glossy and stiff peaks form, about 2 minutes.
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15
Beat in the vanilla extract until just combined.
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16
Spread over the frozen pie and place in the oven until the meringue just browns, 1 to 2 minutes.
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17
Slice and serve.
