Combine oats, milk, water, and salt in a medium saucepan. Bring to a gentle boil over medium-high heat, then reduce to low and simmer for 5 minutes, stirring occasionally, until thickened and creamy but still loose. The oats should look porridge-like with a little movement when you tilt the pan. Remove from heat and stir in the heavy cream. Cover to keep warm.

While the oats simmer, melt the butter in a 10-inch skillet over medium heat. Cook, swirling occasionally, until the butter foams and turns golden brown with a nutty aroma, about 3 to 4 minutes. Watch closely - it goes from brown to burned quickly.

Add the diced apple to the browned butter and cook undisturbed for 2 minutes to build a golden crust. Stir, then add the brown sugar, cinnamon, and pinch of salt. Continue cooking for 4 to 5 minutes, stirring occasionally, until the apples are tender and coated in a glossy caramel sauce. The sugar should be fully melted and bubbling around the edges.

Divide the creamy oatmeal between two bowls. Spoon the warm caramelized apples and all their sauce over the top. Scatter with toasted pecans if using. Serve immediately while the contrast between hot oatmeal and warm apples is at its best.