Preheat oven to 350 degrees F. Line 1 large baking sheet with parchment paper.
Combine the flour, baking powder, and salt in a small bowl.
In a large bowl, cream together the butter and sugar until fluffy. Add the eggs, beating after the addition of each. Add the dry ingredients, alternating with the anisette. Add the vanilla and mix well. Fold in the nuts and aniseeds.
Divide the dough into 2 equal pieces. On a lightly floured surface, roll each under your palms to make a log, about 12-inches in length, and 2-inches in diameter. Place logs on the baking sheets, about 2-inches apart. Bake until golden brown and firm, about 30 minutes. Remove from the oven and let cool completely on the sheet.
Reduce the oven temperature to 300 degrees F.
Transfer the cookie log to a large cutting board and with a heavy knife cut into 3/4-inch thick slices. Spread the cookies on the baking sheet. Bake, turning halfway through cooking, until firm and crisp, about 30 minutes. Remove from the oven and transfer to a wire rack to cool.
In a medium, heavy saucepan, bring the cream, half-and-half, sugar, and zest to a boil, stirring occasionally until the sugar is melted. Remove from the heat.
In a medium bowl, beat the egg yolks until thick and pale, about 2 minutes. In a slow stream, whisking constantly, add about 1 cup of the hot cream mixture to the egg yolks. Beat until well incorporated. Return the yolk mixture to the saucepan with the hot cream and bring to a bare simmer. Cook until a thick custard forms, and the mixture reaches 170 degrees on an instant-read thermometer, about 6 minutes. Remove from the heat and strain through a fine-mesh strainer into a clean container. Stir in the lemon juice and limoncello, and cover with plastic wrap, pressing down against the custard to prevent a skin from forming. Refrigerate until well-chilled, about 2 hours.
Transfer to an ice-cream maker and process according to the manufacturer's instructions. Transfer to an airtight plastic container and freeze until ready to serve.
Yield: 1 quart
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