Preheat the oven to 350°F (175°C).

In a mixing bowl, combine melted butter and brown sugar until smooth.

Spread the mixture evenly in the bottom of the cake pan.

Arrange the pineapple slices on top of the sugar mixture and scatter cranberries evenly over the pineapple.

In a large mixing bowl, cream together softened butter and granulated sugar until light and fluffy.

Add eggs one at a time, mixing well after each addition.

Stir in milk and vanilla extract.

In a separate bowl, whisk together flour, baking powder, and salt.

Gradually add the dry ingredients to the wet mixture, mixing until just combined.

Pour the cake batter over the pineapple and cranberries in the pan.

Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean.

Remove from oven and let cool for 10 minutes.

Invert the cake onto a serving plate and let it cool completely.