First, make the chocolate ganache. Add chopped chocolate or chocolate chips to a small bowl. Add the butter and a pinch of salt. Pour the boiling whipping cream over the mixture and set aside for 2 minutes for the chocolate to melt, then stir with a silicone spatula, to get a silky smooth chocolate mixture. Transfer the mixture to a small baking dish or bowl and place in the freezer for 30 - 40 minutes or to a fridge for at least 2 hours, or overnight.
Chocolate lava cakes mixture
Make the chocolate lava cake mixture. Add chocolate and butter into a heatproof bowl and melt over a pot of boiling water or in 30-second intervals in a microwave. Set aside for 5 minutes. In a large bowl, whisk together the eggs, sugar, and a pinch of salt. Whisk vigorously for 2 minutes, then add the melted chocolate mixture and whisk with a hand whisk until combined and thick. Add the all-purpose flour, cocoa powder, and baking powder. Whisk until well combined. Place in the fridge for 10 - 15 minutes.
Preheat the oven
Preheat the oven to 200 °C / 390 °F or to 180 °C / 355 °F if you are using a convection oven. Grease six aluminum muffin cups. The muffin cups should be about 6 cm (2.5 inches) in diameter and 4 cm (1.5 inches) high. If you are using ramekins/muffin pan grease them, and dust with all-purpose flour or cocoa powder. Make sure to grease the whole interior of the cups.
Fill the cups
Take the chocolate ganache from the freezer. Using a small ice cream scoop or a teaspoon scoop out some chocolate ganache. Shape into six balls, each weighing approximately 30g / 1 ounce. Add a heaped tablespoon of the chocolate lava mixture into a prepared cup, place the ganache ball on top, then cover with the rest of the chocolate lava mixture until 3/4 filled.
Bake and serve
Transfer the cups onto a baking sheet. Place in the preheated oven on the middle rack. Bake for 16 - 18 minutes at 200 °C / 390 °F or at 180 °C / 355 °F if you are using a convection oven. Once the lava cakes are baked, remove them from the oven, set them aside for 1 - 2 minutes, then invert onto a dessert plate and serve immediately. Optionally top with cocoa powder, and shredded chocolate.