Preheat the oven to 350°F (180°C). Line a 12 cavity muffin pan with paper liners.
Melt the 3 oz (90g) semisweet chocolate and butter over a bain-marie until smooth. Let cool slightly.
Meanwhile mix the eggs with sugar, salt, vanilla extract and instant coffee using a whisk or mixer until thick and light yellow, for about 5 minutes.
Add melted chocolate and mix until well combined.
Using a spatula fold in the sifted flour and cocoa powder. Fold in the remaining 2 oz (60g) chocolate chips. Divide the batter equally into muffin cups.
Bake for about 17-20 minutes until puffed and cracked or until a toothpick inserted into the center comes out with a few crumbs attached.
While still warm, add more chocolate chips on top of the muffins, if desired.
Let cool and enjoy!