In a small saucepan, combine frozen berries, honey or maple syrup, and vanilla extract. Cook over medium-low heat for about 5-10 minutes until thickened, mashing the berries if you'd like.

In a medium saucepan, bring water and salt to a boil. Add in the old-fashioned oats, then reduce heat and let them simmer for 5-8 minutes, stirring occasionally until the oats are tender and creamy.

In a bowl, whisk the eggs until they turn pale yellow. Stir in the cold milk into the cooked oats, then gradually whisk in the eggs while cooking over low heat for an additional 1-1.5 minutes until the mixture thickens.

Spoon the custard oats into bowls and generously top with the mixed berry compote. Optionally, add nuts or a dollop of yogurt.