Preheat the oven to 350°F (175°C). Grease a 9-inch round cake pan and line the bottom with parchment paper.
In a microwave-safe bowl, melt the chocolate chips and butter together in the microwave, stirring every 30 seconds until smooth.
Alternatively, you can melt them together in a heatproof bowl set over a pan of simmering water.
Stir in the sugar, salt, and vanilla extract until well combined.
Add the eggs one at a time, mixing well after each addition.
Pour the batter into the prepared cake pan and smooth the top.
Bake for 25-30 minutes or until the edges are set and the center is slightly jiggly.
Allow the cake to cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.
Dust with powdered sugar or cocoa powder before serving, if desired.