Ingredients:

For the cookie dough:

¾ cup (170g) unsalted butter, at room temperature

1 cup (200g) granulated sugar

1 teaspoon (3g) lemon zest (about 1 lemon, zested)

1 (50g) large egg, at room temperature

2 teaspoons (8.4g) vanilla extract

⅓ cup (80g) sour cream 

¼ teaspoon (1.3g) baking soda, sifted

2 cups (311g) Sequoia flour or 2 cups (292g) Organic Edison 

½ teaspoon (2.5g) fine sea salt

1 teaspoon (3.8g) baking powder

For the frosting:

2 cups (250g) icing sugar* (see Baker’s Notes)

4-5 tablespoons (60-75g) milk, divided

1 pinch of sea salt

1 tablespoon (22g) Lyles golden syrup** (see Baker’s Notes)

1 teaspoon (4.2g) vanilla extract

¼ cup (25g) dutch cocoa powder or unsweetened cocoa powder, sifted

Instructions:

1. Preheat the oven to 375°F with a rack positioned in the center of the oven. 
2. Prepare 2 sheet trays lined with parchment paper or a silpat. 
3. In a bowl of an electric stand mixer fitted with a paddle attachment, combine the butter, sugar and lemon zest. Cream together for 3-5 minutes, until light and fluffy. 
4. In a separate bowl, whisk together the egg and vanilla extract.
5. Scrape down the sides of the stand mixer bowl and add the egg and vanilla mixture. Mix for 1 minute until well incorporated.
6. In a small bowl, combine the sour cream and sifted baking soda, lightly stir together until it begins to lighten in texture.
7. Scrape down the sides of the stand mixer bowl and add the aerated sour cream to the mixture. Mix until just combined.
8. In a medium-size bowl, combine the flour, sea salt and baking powder. Using a whisk, blend together so they are evenly distributed. 
9. Add the flour mixture to the stand mixer bowl and mix until just combined.
10. Using a lightly greased ¼-cup measuring cup, scoop the cookie dough into circular mounds on the prepared sheet trays. Each tray should fit 6 cookies evenly spaced apart. 
11. Bake in the oven for 10 minutes. Turn the sheet tray around 180 degrees and bake for another 5 minutes until the cookies are evenly baked and golden brown on the edges. 
12. Allow to cool on the cookie sheet for 1-2 minutes. Transfer the cookies to a wire cooling rack and cool to room temperature.
13. Repeat the baking process for the second sheet tray of cookie dough.
14. While the cookies are baking and cooling, make the frosting.
15. Position a large sifter in the center of a medium-size bowl. Measure the icing sugar right into the sifter and sift the sugar into the bowl until no lumps are present. 
16. Add 3 tablespoons (45g) of milk, a pinch of sea salt and golden syrup to the confectioner’s sugar. Using a whisk combine the ingredients together until you have a thick yet fluid frosting. 
17. Pour about ½ the frosting into a separate bowl.
18. To make the vanilla frosting, add the vanilla extract to one of the bowls and set aside. 
19. In the other bowl of frosting, add the sifted cocoa powder and 1 tablespoon of milk and whisk until shiny and no lumps are present. If it seems too dry, you can add a little more milk.
20. Once the cookies have cooled, turn them upside-down and, using an offset spatula or butter knife, frost the flat, back side of each cookie with ½ chocolate and ½ vanilla frosting.
21. Be sure to cover the frosting bowls with a lightly damp towel or plastic wrap so the frosting does not harden as you frost each cookie.
22. Allow the frosting to set for at least 15-30 minutes before eating.