Preheat oven to 350°F. Spread the pistachios on a baking sheet into a single layer. Bake for 10 minutes or until the nuts are lightly toasted.
Cream together the butter and sugar until light and fluffy. Add the eggs one at a time, mixing after each. Mix in the vanilla. Add the flour, baking powder, salt and lemon zest and mix until just combined. Fold in the pistachios.
Divide the dough in half. Form each into a log 12 inches long and 1 inch tall on a sheet pan lined with parchment paper. Bake for 35 minutes or until the bottoms are just starting to brown. Let the logs cool for 5 minutes, then slice on a diagonal into 12 1-inch slices. Put the cookies back on the sheet pan and bake for 8 minutes, then flip over and bake on the other side for 8 minutes. Cool completely on a wire rack.
I dipped a few of mine in white chocolate and they were amazing!