Place pistachios in a food processor and pulse until pistachios are ground into a fine crumb. Sift pistachios through a wire mesh sieve and return any larger pieces to the food processor and pulse again. Repeat until there is 1/2 cup of fine pistachio crumbs. Set aside.

In a medium-sized bowl, mix together the white sugar and vegetable oil.

Beat in the eggs, until fully incorporated.

Stir the dry ingredients into the wet mixture just until combined (do not over beat). Cover bowl with wrap and refrigerate for at least 4 hours or overnight.

When ready to bake, preheat oven to 350°F | 175°C. Line 2 cookie sheets or baking trays with parchment paper (baking paper). Roll 1 tablespoonful of dough into balls for smaller cookies, or 2 tablespoonfuls for larger cookies.

Add the confectioners (icing) sugar to a smaller bowl. Evenly coat each ball of dough in confectioners' sugar to form a balls and place onto prepared cookie sheets.

Bake in preheated oven for 12 minutes (for small cookies) or 14 minutes (for larger cookies) or until cookies are set and begin to brown around the edges. The cookies will come out soft from the oven but will harden up as they cool.

Allow to cool on the cookie sheet for 5 minutes before transferring to wire racks to cool.