Pour whole milk into a large saucepan and heat over medium heat, stirring continuously until it reaches around 195°F, just before boiling.

In a separate bowl, whisk together all-purpose flour, granulated sugar, and kosher salt until smooth.

Melt salted butter in a small saucepan over low heat, keeping it from burning.

Add the melted butter to the dry mixture and stir until a smooth paste forms.

Gradually whisk the paste into the heated milk, then increase the heat to gently boil. Simmer on low for about 5 minutes.

Spoon the thick and creamy Rømmegrøt into warm bowls and drizzle with melted butter and sprinkle with cinnamon-sugar.