Preheat oven to 450℉. Butter eight 8-oz. ramekins
Place butter, chocolate and powdered espresso in a saucepan and cook over low heat until melted. Remove from heat and cool for 2-3 minutes.
Blend eggs and eggs yolks in a bowl, using a wire whisk. Stir in the sugar, vanilla, and the chocolate mixture. Whisk to blend. Add flour and whisk again to incorporate. Evenly distribute the batter among the 8 prepared ramekins.
Either bake the lava cakes immediately, or cover with plastic wrap and store in the refrigerator for up to 1 day ahead.
Bake cakes until sides are set, but the center is still soft and gooey, 8-10 minutes, depending upon whether the batter was refrigerated or at room temp.
To loosen cakes, run a knife around the edges of the ramekin and invert onto a dessert plate. Serve with a spoonful of your favorite frozen concoction, or a spoonful of yogurt whipped cream*.
*To make yogurt whipped cream, beat 1 cup of heavy cream to stiff peaks. Gently fold in 1 cup of nonfat plain Greek yogurt. Sweeten with a tbsp. of light agave syrup or 2 tbsp. powdered sugar, and flavor with 1 tsp. pure vanilla extract.