Preheat the oven to 450°F. Butter and flour 6 (6-ounce) ramekins. Place on a rimmed baking sheet and set aside.
In a medium, microwave-safe bowl, combine the butter and chocolate. Microwave at 50% power until the mixture is smooth and melted, about 90 seconds, stirring every 30 seconds. Set aside.
In the bowl of a stand mixer fitted with a whisk attachment, combine the eggs, yolks, sugar, vanilla, instant espresso granules, and salt. Beat on medium-high until thick and pale, about 3 minutes.
Immediately fold the warm chocolate mixture and flour into the whipped egg mixture. Divide the batter evenly among the prepared ramekins. (A heaping ⅓ cup should go in each).
Bake until the sides of the cakes are set, but the centers are still slightly jiggly, 7 to 9 minutes. Let the cakes cool in the ramekins for 1 minute. Invert each cake onto a serving plate. Serve immediately with ice cream, chocolate or caramel sauce, and halved strawberries.