Preheat the oven to 175 C and grease a 9x5 loaf tin or line it with non-stick baking paper, leaving an overhang for easy removal.
Sift the flour, baking powder and salt in a bowl. Set aside.
In a mixing bowl, beat the butter and sugar with a hand mixer until pale and fluffy. Add the honey, orange zest and vanilla and beat briefly.
Add the egg and beat until incorporated into the batter.
Now add half the flour mixture and half the yoghurt (this prevents the batter from splitting) and beat on low speed. Then add the remaining yoghurt and flour mixture, beating again to combine into a smooth, thick-ish batter.
Fold in the chocolate chips and walnuts, then transfer the batter to the prepared loaf tin. Smoothen the top and bake for 40 to 45 mins until a toothpick poked in the center comes out clean. Let the cake cool in the tin for 15 minutes, then remove and place on a wire rack to cool completely.
Store in an airtight tin at room temperature for 2 to 3 days, after which it is best kept in the fridge (in humid places) for a week. The cake is on the denser side because of the rye flour, so lightly reheating the pieces will bring them back to the original texture. Happy baking!