PREHEAT oven to 350F. Line a 9 × 13-in. baking dish with parchment paper. Stir flour with baking powder, baking soda, 1/2 tsp cinnamon, cloves and salt in a medium bowl. Set aside.
BEAT oils with shortening and 1/2 cup sugar in a stand mixer fitted with a paddle attachment on medium-high until creamy, about 5 min. Add egg yolk and continue to beat for 2 more min.
REDUCE speed to medium-low and beat in half of zest and half of flour mixture until combined (reserve remaining zest for honey syrup). Beat in juice, then remaining flour mixture, just until combined. Do not over-mix.
STIR walnuts with 2 tsp cinnamon in a small bowl.
SPREAD half of dough on bottom of prepared dish. The layer will be thin. Sprinkle with half of walnut mixture. Break off pieces of remaining dough and place on top of walnut mixture. It should be about the same thickness as bottom layer. Don’t worry if it’s not perfect, but it should cover nuts. Stir pistachios into remaining walnut mixture, then scatter overtop.
BAKE in centre of oven until golden, 20 to 22 min.
COMBINE honey-syrup ingredients with 1/3 cup water in a medium saucepan and set over medium-high. Bring to a boil, then reduce heat to mediumlow. Simmer until syrup coats the back of a spoon but is still runny, about 15 min. Remove from heat, discard cinnamon stick and stir in remaining zest.
REMOVE baking dish from oven. Run a knife around the edges of pan, then cut into diamond-shaped bars. Drizzle syrup evenly overtop. Let cool completely on a rack. Lift parchment paper out of dish. Retrace diamond pattern, then remove bars to a serving tray. Store in an airtight container up to 1 week.
How to candy walnuts
Nutrition (per serving)
From the kitchen of Christina Frantzis (kitchen intern).
Make Ahead Tip: These bars are even tastier a few days after they are baked.