Banana Upside-Down Cake

Ingredients:
• 6 to 8 ripe bananas (whole and peeled)
• 3 eggs
• 200 g sugar
• 120 g melted butter
• 200 ml milk
• 250 g flour
• 1 sachet baking powder (10 g)
• 1 pinch salt •
1 teaspoon vanilla extract (optional)
• Butter and sugar for the mold (optional, for caramelizing)