Apply 1 T of softened butter to sides and bottom of ramekins using a pastry brush.
In a small microwaveable bowl, melt 7 T butter and chocolate until smooth and combined by microwaving in 30-second intervals, to avoid burning chocolate.
In a medium bowl, whisk eggs, yolks, powdered sugar and salt until sugar is dissolved. Add chocolate mixture and stir with a spatula until blended.
Add flour and fold with spatula until smooth. Do not overwork.
Divide evenly between four ramekins (or muffin cups). Place a tablespoon of dulce de leche in center of each filled ramekin. Place ramekins on baking sheet then refrigerate at least 2 hours.
Preheat oven to 375 degrees. Place ramekins in oven and bake approx. 18 min, rotating halfway through baking, until cakes rise and a thin crust has formed. Remove from oven and let cool approx. 5 minutes. Then do one of the following, depending on the mold used.
For ramekins: Invert each ramekin onto a serving plate, gently unmold and serve. Or cool, wrap individually and put in freezer.
For foil muffin pan: Cut "cups" apart with scissors and invert onto plates to serve. Or cool, wrap individually and put in freezer.
For regular muffin pan: Place the baked cakes in refrigerator 2-3 hours or overnight. When ready to serve, place the pan in a dish with some hot water, gently release the cakes with a butter knife and remove. Invert onto a serving plate and microwave 30-45 seconds to melt the center. If freezing, remove from pan, wrap individually and place in freezer.
To serve cakes after they're frozen: Thaw for 2 hours, then invert onto a serving plate and microwave 30-45 seconds on high, until the center melts.
*Callebaut bittersweet chocolate is available in your Market Bakery retail section.
**Dulce de leche is a South-American milk confection that's similar to caramel but thicker and richer. Find it in your Market Cheese Shop.