Preheat your oven to 350°F (175°C). Roll out thawed puff pastry in an 8- or 9-inch tart pan and refrigerate.

In a skillet, melt butter over medium-high heat and cook bacon until crispy, about 6-8 minutes. Transfer to paper towels.

Add onions to the skillet and cook for 3-4 minutes until translucent. Add potatoes and dill, seasoning with salt and pepper. Cook for another 3-5 minutes without fully cooking potatoes.

Remove from heat and spoon the bacon and potato mixture into the crust. Drizzle heavy cream over filling and level the top with a spatula.

Bake in the oven for 35-45 minutes, until potatoes are fork-tender and the crust is golden brown.

Let the pie rest for 10 minutes. Garnish with chopped chives or scallions, slice, and serve warm.