In a small saucepan, combine frozen mixed berries, honey or maple syrup, and vanilla extract. Heat over medium-low, stirring until it simmers. Allow to thicken for about 10-12 minutes, mashing berries with a fork to enhance flavor.

In a medium saucepan, mix old-fashioned oats, water, and a pinch of salt. Bring to a boil over medium-high heat, then reduce to low and simmer, stirring frequently for 5-8 minutes until absorbed and creamy.

Whisk large eggs in a bowl. Once oats are tender, remove from heat, stir in cold milk, and gradually add eggs while stirring to prevent scrambling. Return to low heat for about 1-2 minutes until thickened.

Serve by spooning custard oats into bowls and generously topping with mixed berry compote. Add optional toppings like sliced almonds or cinnamon.