3/4cup (168g)unsalted butter, diced into 1 Tbsp pieces, plus more butter for pan
1 1/2cups (190g)powdered sugar
1/2cup (70g)all-purpose flour
Vanilla ice cream, sweetened whipped cream, raspberries, chocolate sauce or caramel sauce for serving
Preheat oven to 425 degrees. Butter 6 wells of a jumbo muffin pan or six 6 oz. ramekins with softened butter (cover well you don't want these to stick), set aside.
Place chocolate and butter in a medium microwave safe mixing bowl and heat in microwave in high power for 30 seconds, remove and stir.
Return to microwave and heat 30 seconds longer, stir well. If it's still not melted continue to heat in 15 second intervals until melted. Let cool slightly.
Stir in powdered sugar and salt (it will be thick at this point) then mix in eggs, egg yolks and vanilla (it will take a bit of stirring to get them fully incorporated). Stir and fold in flour until combined.
Divide batter among prepared muffin wells, filling each about 2/3 full (about 1/2 cup in each. If using custard cups transfer them to a baking sheet to bake).
Bake in preheated oven until edges are set but center is still soft, about 11 - 12 minutes.
Remove from oven and cool 1 - 2 minutes (run a knife around edge if they don't seem loose), invert onto a cutting board or other rectangular surface then transfer to dessert plates and top as desired, serve warm.