Heat butter in a small skillet over medium-low heat, stirring continuously until it turns brown (3-4 minutes).

Turn off the heat and set the browned butter aside.

In a mixing bowl, combine milk, eggs, and almond essence and whisk until well blended.

In a separate mixing bowl, combine all-purpose flour, demerara sugar, baking powder, and salt.

Add orange zest to the flour mixture and rub it in with your fingers to release its flavor.

Pour the egg-milk mixture into the dry ingredients and whisk until you have a smooth batter.

Whisk in the browned butter into the batter.

Preheat oven to 180 degrees Celsius (350 degrees Fahrenheit).

Grease a 10-inch skillet with soft butter.

Pour the cake batter into the greased skillet.

Arrange the thinly sliced plums on top of the batter.

Bake in the preheated oven for 30-35 minutes, or until a skewer inserted into the center comes out clean.

Remove from the oven and let the cake cool slightly before serving.

Serve warm, optionally with a scoop of vanilla ice cream and caramel sauce or coffee.