Preheat oven to 350 degrees F.
Place pecans in a 9-inch pie pan and toast in oven about 5-7 minutes, or until pecans are deep brown and glossy. Watch carefully so pecans don’t burn. Chop finely and set aside.Sift together flour, baking powder and salt. Set aside.
In large mixing bowl, combine butter and sugar and beat on medium speed until light and fluffy. Beat in vanilla, egg and orange zest. Fold in dry ingredients and nuts and mix until thoroughly blended.
Line a baking pan with parchment paper. Form dough into a 3″ x 12″ strip. Mound dough up slightly in center of strip so that sliced biscotti will be slightly thicker in the middle.
Bake on middle rack until light golden, about 18-20 minutes. Remove pan from oven and let cookie loaf cool 10 minutes. Reduce oven temperature to 300 degrees F.
Either on the pan or on a cutting board, slice loaf of dough diagonally into 1/4-inch slices. You should have between 12 and 16 slices. Turn slices so that cut-side is down. Spread out evenly on pan.Return pan to oven and bake 20 minutes, turning cookies over halfway through baking. Turn off oven and let cookies cool 1 – 2 hours in oven with heat off. They should be quite crisp. Store in airtight container.