Dazzley's Kladdkaka

Ingredients
For the Mud Cake
250 g (9 oz / 1 cup) unsalted butter, roughly chopped
200 g (8 oz) dark chocolate block, roughly chopped
1 cup (240 g) caster sugar / superfine sugar
1 cup (220 g) brown sugar, packed
1 teaspoon (3 g) instant coffee granules, optional
1 ½ cups (375 mL) milk
3 large eggs (approx. 55 g / 2 oz each)
1 tablespoon (20 g) vanilla essence OR 2 teaspoon (10 g) vanilla extract
1 ½ cups (225 g) plain / all-purpose flour
½ cup (50 g) unsweetened cocoa powder
1 tablespoon (16 g) baking powder
1 teaspoon (5 g) salt
For the Chocolate Ganache
¼ cup (63 mL) thickened (pouring) cream
¼ cup (63 mL) milk
200 g (8 oz) dark chocolate block, finely chopped