1. Preheat the Oven:

• Preheat your oven to 325°F (160°C). Grease and flour two 8-inch (20cm) round cake pans and set them aside.

2. Prepare the Wet Ingredients:

• In a small bowl, whisk together the milk and Greek yogurt, then set aside.
• In the bowl of a stand mixer, cream the softened butter on medium speed until it becomes silky and smooth, about 4-5 minutes.
• Add the honey and continue to beat for another 1-2 minutes, or until the mixture is light and fluffy. Add the vanilla extract and orange zest, beating just until combined.

3. Incorporate the Eggs:

• Scrape down the sides of the bowl, then add the eggs and egg yolks one at a time, ensuring each is fully incorporated before adding the next. Stop to scrape down the bowl after each addition.

4. Combine Dry Ingredients:

• In a separate bowl, sift together the cake flour, baking powder, baking soda, and salt.

5. Mix the Batter:

• Remove the bowl from the stand mixer. Alternating in thirds, fold the milk mixture and the dry ingredients into the butter mixture using a spatula. Be careful not to overmix—fold just until combined.

6. Bake the Cakes:

• Divide the batter evenly between the two prepared cake pans. Run a knife through the batter to remove any air bubbles, then drop the pans from a few inches above the counter to further eliminate bubbles.
• Bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean. Watch closely toward the end of baking as the honey can cause the cakes to brown quickly.

7. Cool the Cakes:

• Let the cakes cool in the pans for 5-10 minutes. Run a knife gently around the edges, then invert the cakes onto a wire rack to cool completely.

8. Prepare the Frosting:

• In the bowl of a stand mixer, beat the heavy whipping cream until soft peaks form. Add the elderflower liqueur and beat for an additional 30 seconds.
• In a separate bowl, beat the mascarpone until soft and fluffy, about 2 minutes. Fold the mascarpone into the whipped cream mixture until fully combined.
• In a small bowl, mix 1 1/2 cups of the cream mixture with the blackberry jam and set aside.

9. Assemble the Cake:

• Place one cake layer on a serving plate or cake stand. Spread the blackberry mixture on top, leaving about 1/2 inch (1.3cm) between the filling and the edge to prevent it from oozing out.
• Place the second cake layer on top and spread the remaining mascarpone frosting over the top.

10. Prepare the Honeycomb Brittle:

• Coat a baking sheet with vegetable oil spray. In a medium saucepan, combine the sugar, honey, and water, and bring to a boil over medium-high heat without stirring until the mixture reaches 300°F (150°C) on a candy thermometer.
• Remove from heat and quickly stir in the baking soda with a whisk. Pour the mixture onto the prepared baking sheet and let it cool completely before breaking into pieces.

11. Garnish and Serve:

• Sprinkle the honeycomb brittle over the frosted cake. For the best presentation, garnish the cake just before serving.