Banana Nut Bundt Cake

• 4 oz unsalted butter, diced, plus extra to grease
• 7 oz dark brown sugar
• 7 oz ripe bananas, in pieces
• 2 oz buttermilk
• 1 tsp vanilla extract
• 2 large eggs
• 7 oz all-purpose flour
• 1 tsp baking soda
• ½ tsp salt
• 3 oz chopped pecans

Caramel Sauce

• 9 oz sugar
• 7 oz heavy whipping cream, divided
• 36 oz water, divided
• 1 ½ oz unsalted butter, divided, 1 oz cold, in 1 cube (1 in.) and 0.5 oz room temperature
• 1 tsp lemon juice
• 1 tbsp vinegar
• chopped pecans, to garnish