Chop chocolate coarsely around the size of chocolate chips.
Preheat the oven to 400 degrees F. Cut butter into 8 tablespoons. Set aside 1 tablespoon and add the remaining 7 tablespoons to a large microwave-safe bowl with the chocolate. Microwave for 45 seconds then stir until smooth, about 1 minute of stirring. Set aside to cool.
In a large bowl add eggs and egg yolks. Let stand to get to room temperature. Add in brown sugar and whisk vigorously until smooth and slightly thickened about 1 minute. Add in salt, vanilla, and cooled chocolate mixture. Whisk until smooth and combined. Add in flour and whisk until just combined. Do not over mix here, just about 30 seconds.
Using the remaining 1 tablespoon butter. Rub across 7 cavities of the muffin tin. I stick my hand in a plastic sandwich bag and rub the butter to really well coat the muffin tin. You should use all the butter and be sure to get the base of each cavitiy well. Sprinkle lightly with cocoa powder and then shake around to coat all of the muffin tin. Tap the muffin tin upside down over the sink to release any extra cocoa powder.
Spoon batter into each of the 7 muffin cavities until about 1/3 full. Place an unwrapped Lindt ball into the center of each cavitiy. Top with more batter dividing the rest evenly among the 7 cavities. Smooth the top with the back of a spoon or your finger.
Bake for 16 to 17 minutes, or until the tops spring back when lightly pressed.
Remove and let muffin tin stand for only 2 minutes. Then place a tray (larger than the muffin tin) on top of the cakes and flip over. Let stand for about 30 seconds then careflly pull up the muffin tin. The cakes should have all released nicely. Use a metal spatula to remove one cake at a time onto a plate. Immediately top with a scoop of vanilla ice cream and then some chocolate shell. Dig in while they're hot and gooey!
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Notes
Note 1: A good muffin tin makes all the difference for a clean release. This one is my favorite. Take your time greasing the pan so the cakes release easily.Note 2: After a lot of testing, these are my favorites for a soft, molten center. Use any Lindt flavor you like, but milk chocolate (red bag) is my family’s favorite.Note 2: The better the chocolate, the better the flavor. Be sure to use semi-sweet chocolate. Most bars are 4 ounces, so you’ll need two bars (and have chocolate leftover). Once chopped, it equals about a heaping 1 cup. Use the extra chocolate to shave curls on top for a fancy finish. A veggie peeler works great for this.Storage: Lava cakes are best served fresh. If needed, cool completely, then store tightly wrapped in the fridge for up to 2 days. Reheat gently in the microwave. Centers may not be molten.