Preheat the oven to 350°F (175°C). Press thawed puff pastry into an 8 or 9-inch tart pan and chill in the refrigerator.

In a large skillet, melt 2 tablespoons of unsalted butter over medium-high heat, cook thick-cut bacon for about 5-7 minutes until crispy.

In the same skillet, sauté sliced onions for 3-4 minutes. Add thinly sliced potatoes and fresh dill, seasoning with salt and pepper, cook for another 3-5 minutes.

Transfer the sautéed potato mixture to the tart crust, drizzle heavy cream over the mixture.

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

Let the pie rest for about 10 minutes and then garnish with fresh chives or scallions before serving.