Preheat the oven to 350°F (180°C). Butter and line with parchment a 9-inch (23cm) springform pan. Set aside.

In a large bowl whisk together the melted butter, cocoa powder, granulated sugar, brown sugar and the Guinness.

Whisk in the sour cream, and then the eggs and vanilla extract until fully combined.

In a separate bowl, combine the flour, baking soda, and salt. Whisk the flour mixture into the chocolate mixture until evenly mixed.

Pour the batter into the prepared pan and bake for 45-60 minutes, until a skewer inserted in the middle comes out clean. Let the cake cool completely in the pan.

While the cake is cooling, prepare the butter glaze: combine the butter, chocolate, and honey in a microwave-safe bowl or in a small saucepan and heat gently until the butter and chocolate melt. Stir together and let cool until thickened but still pourable.

Once the cake has cooled, transfer the cake to a serving plate and pour the glaze on the cake. Let the glaze set for an hour or two before serving if you wish.

Store any leftover cake in an airtight container at room temperature for up to 3 days. For longer storage, freeze in an airtight container for up to 2 months.