Heat the oven to 400°F. Chop the 5 ounces of semi-sweet chocolate coarsely, about the size of chocolate chips.

Cut the butter into 8 tablespoons and set 1 tablespoon aside for the pan. Put the other 7 tablespoons in a large microwave-safe bowl with the chopped chocolate. Microwave for 45 seconds, then stir for about 1 minute until smooth. Set the bowl aside to cool.

Put the eggs and egg yolks in a large bowl and let them stand until they come to room temperature. Add the brown sugar and whisk hard for about 1 minute, until smooth and slightly thickened. Whisk in the salt, vanilla and the cooled chocolate mixture until smooth. Add the flour and whisk for about 30 seconds, just until combined. Do not overmix.

Rub the reserved 1 tablespoon of butter over 7 cavities of the muffin tin, covering the base of each one well (a hand inside a plastic sandwich bag makes this easy). Sprinkle lightly with cocoa powder and shake the tin to coat it. Tap the tin upside down over the sink to knock out the extra cocoa.

Spoon the batter into the 7 cavities until each is about 1/3 full. Set one unwrapped Lindt ball in the center of each. Top with the rest of the batter, dividing it evenly, and smooth the tops with the back of a spoon or a finger.

Bake for 16 to 17 minutes, until the tops spring back when lightly pressed.

Let the muffin tin stand for only 2 minutes. Set a tray larger than the muffin tin on top and flip it over. Let it stand for about 30 seconds, then carefully lift the muffin tin off. Use a metal spatula to move one cake at a time to a plate.

Right away, top each cake with a scoop of vanilla ice cream and some chocolate shell. Serve while they are hot and gooey.