Preheat your oven to 425°F (220°C). Grease four 6-ounce ramekins with butter and lightly dust them with cocoa powder to prevent sticking.
In a microwave-safe bowl, combine the chopped chocolate and butter. Microwave in 20-second intervals, stirring after each, until smooth. Set aside to cool slightly.
In a separate bowl, whisk together the eggs, egg yolks, powdered sugar, vanilla extract, and salt until light and fluffy. Gradually fold in the melted chocolate mixture. Sift in the flour and gently mix until fully combined.
In a small bowl, mix the strawberry jam and finely chopped strawberries. Divide half of the cake batter between the ramekins. Spoon about 1 teaspoon of the strawberry filling into the center of each, then cover with the remaining batter.
Place the ramekins on a baking sheet and bake for 10-12 minutes, until the edges are firm but the center is slightly soft. The cakes should still have a molten, gooey center.
Let the lava cakes cool for 1-2 minutes, then run a knife around the edges and carefully invert them onto plates. Dust with powdered sugar, add fresh strawberries, and serve with whipped cream or vanilla ice cream.