Preheat your oven to 175°C (350°F) and line a 12-cup muffin tin with cupcake liners.

In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.

In a large bowl, beat 115g softened butter and caster sugar with an electric mixer until light and fluffy, about 3-4 minutes.

Add the eggs one at a time, beating well after each addition. Mix in the vanilla bean seeds until combined.

Combine the milk and sour cream in a small jug.

Alternately add the flour mixture and milk mixture to the butter mixture in three additions, beginning and ending with flour. Mix until just combined.

Divide the batter evenly among the cupcake liners, filling each about two-thirds full.

Bake for 20-22 minutes until a toothpick inserted into the center comes out clean and tops spring back when lightly touched.

Remove from oven and let cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.

For the frosting, beat 225g softened butter until creamy. Gradually add cocoa powder and icing sugar, alternating with 3 tbsp milk, beating until smooth. Add vanilla extract.

Gently fold the marshmallow fluff into the chocolate frosting, creating a marbled effect rather than fully mixing.

Pipe or spread the frosting generously onto the cooled cupcakes using a large round tip or offset spatula.

Top each cupcake with a mini marshmallow and use a kitchen torch to toast the marshmallow until golden brown, or place under a hot grill for 30-60 seconds watching carefully to prevent burning.

Serve immediately or store in an airtight container at room temperature for up to 2 days.