Make the cake batter

1. Preheat your oven to 160°C fan (350°F). 
2. Prepare an unlined a 6-inch tube pan. Do not grease it.
3. In a bowl, whisk together the cocoa powder and hot milk until smooth. Set aside to cool slightly.
4. In a separate large bowl, whisk the egg yolks and 40g sugar until pale and slightly thickened.
5. Add the vegetable oil, and vanilla extract,  mix well.
6. Pour in the cooled chocolate mixture and whisk until combined.
7. Sift in the cake flour, salt and baking powder, then gently mix until smooth.

Make the Meringue

1. In a clean, grease-free bowl, add lemon juice and whisk the egg whites with a hand mixer until foamy.
2. Gradually add 42 g sugar, one-third at a time, beating until stiff peaks form.

Combine the Mixtures

1. Take around one-third of the meringue and fold it into the egg yolk batter to lighten it.
2. Gently fold in the remaining meringue in two additions, using a spatula to maintain the airy texture.
3. Pour the batter into the unlined chiffon pan and shake the pan to smooth the top.
4. Lift the pan up a few inches and drop it against the work surface to release any trapped air bubbles.  Also, run a skewer into the batter to get rid of the small air pockets to achieve the smooth crumb. 
5. Bake at 160°C fan (350°F) for 35 minutes, or until the top is set and a skewer inserted comes out clean.

Cool the Cake

1. Immediately invert the cake pan and let the cake cool completely upside down to prevent collapse.
2. Once cooled, run a knife around the edges to release the cake.

Make the Chocolate Ganache (optional)

1. Place the chopped chocolate in a microwave-safe bowl and add the double cream.  Microwave it for 20 seconds and give it a good stir. Then continue to microwave it for a few 5-second bursts until the chocolate is fully melted.
2. Stir in butter gently for extra shine.  Let the ganache cool slightly until it thickens but is still pourable.

Decorate the Cake (optional)

1. Place the cooled chiffon cake on a wire rack over a baking tray to catch any excess ganache.
2. Slowly pour the ganache over the top of the cake, letting it drip down the sides naturally. Use a spoon to spread evenly if needed.
3. Coat the fresh strawberries with the ganache and sprinkle with chopped pistachios.  
4. Slice and serve—enjoy your beautifully decorated Chocolate Chiffon Cake with Ganache & Strawberries!