Preheat your oven to 350°F (175°C) and fit the thawed frozen puff pastry into an 8 or 9-inch tart pan, trimming excess pastry.

In a skillet over medium heat, melt a tablespoon of butter, add thick-cut bacon, and cook until crispy, about 5–7 minutes. Transfer bacon to paper towels.

Using the bacon drippings, sauté sliced onions in the same skillet until softened, about 3–4 minutes. Add sliced potatoes and dill, seasoning with salt and pepper. Cook for an additional 3–5 minutes.

Layer the sautéed potato mixture into the prepared puff pastry, crumble crispy bacon over potatoes, and pour heavy cream evenly.

Bake on the lower rack for 35–45 minutes, checking for fork-tender potatoes and a golden brown crust. The filling should bubble at the edges.

Allow the pie to rest for 10 minutes before garnishing with chopped chives or scallions.