A combination of semolina and all-purpose flours gave the shortbread crust a rich, crumbly texture and complex flavor. Chilled butter prevented the dough from getting overly sticky, but if your kitchen is particularly warm and the dough is soft and shiny after mixing, refrigerate it for 30 minutes before proceeding. Covering the dough with plastic while making the filling and rolling it out between sheets of kitchen parchment further prevent the dough from drying out. If the dough begins to crack while shaping the cookies, gently pinch the cracks back together. You can substitute pistachios for the walnuts, but the filling will take an extra minute or so to come together into a paste. While rose water is traditional, we found a good substitution: 2 teaspoons each of orange juice and orange zest, plus 1/4 teaspoon almond extract. These cookies keep for up to three days in an airtight container at room temperature.