Preheat your oven to 350°F (175°C) and grease two ramekins with butter.
In a mixing bowl, combine the flour and cocoa powder, whisking to eliminate lumps.
In another bowl, mix melted butter and brown sugar until well combined. Add the egg and whisk until smooth.
Gradually incorporate the dry ingredients into the wet mixture, followed by the milk, stirring gently.
Fold in the chocolate chips and divide the mixture evenly between the prepared ramekins.
Bake in the preheated oven for about 15-20 minutes until the tops are set but the centers remain soft.
For the toffee sauce, combine brown sugar and heavy cream in a saucepan over medium heat, stirring until dissolved. Simmer for 5 minutes until thickened.
Invert the puddings onto plates and drizzle with warm toffee sauce. Serve with ice cream or whipped cream if desired.
Notes
For variations, consider adding a pinch of sea salt to the toffee sauce or incorporating nuts into the batter.