Limoncello-Pine Nut Biscotti

1 cup all-purpose flour
1/2 cup granulated sugar, plus a bit extra
A pinch of salt
1/2 teaspoon baking powder
3 tablespoons cold, unsalted butter, cut into tiny pieces,
    plus extra for buttering the pan
1 large egg
1 teaspoon pure vanilla extract
Zest of 2 large lemons
2 tablespoons limoncello (lemon liqueur)
3/4 cup toasted pine nuts

Heat the oven to 350 degrees F. Butter a cookie sheet.

Place the flour, sugar, salt and baking powder in the bowl of a food processor and pulse briefly to blend. Add the chopped butter and pulse briefly a few times, just until the butter is broken down into very tiny bits.

In a small bowl, whisk together the egg, vanilla extract, lemon zest and limoncello. Add this and the pine nuts to the food processor and pulse very briefly, just to blend. The mixture should be moist but crumbly. Turn it out onto a flat surface and press it together. Press the dough away from you using the palm of you hand once or twice so everything is well moistened. Form the dough into a ball. Cut the dough in half and roll each section into a 1-inch-thick rope. If the dough seems too sticky, dust your hands with flour while rolling it. Place the two ropes on the sheet pan a few inches apart. Flatten the tops slightly. Sprinkle lightly with sugar and bake until very lightly golden, about 30 minutes. Remove from the oven and let sit for about 5 minutes to cool slightly (if the logs are too hot when you try to slice them, they can break).

When the two ropes are cool enough to remove from the sheet pan without breaking, place them on a flat surface and cut into approximately 1/4 inch slices, cutting on an angle using a quick, clean stroke with a sharp chef's knife (don't try a sawing motion or you may cause the biscotti to break up). Place the cut biscotti, cut side up, back on the sheet pan, and bake for about 10 minutes longer, or until they are lightly browned.

When cool, store in a covered container. They will keep about one week.