Wash and boil the potatoes in salted water until fork-tender, 25-30 minutes. (It may take longer, depending on the size of the potatoes.)
Preheat the oven to 350°F and line a large baking sheet with parchment paper.
Drain the potatoes, pat them dry, and place them on the lined baking sheet.
Use the bottom of a glass to smash the potatoes to about ¼-inch thick.
In a small bowl combine melted butter, garlic, and Cajun seasoning.
Brush the smashed potatoes with the butter mixture, reserving some to brush on after flipping over the potatoes.
Bake 30 minutes.
After 30 minutes, flip over the potatoes and brush the remaining butter mixture over the tops of the potatoes.
Bake for 25-30 additional minutes, or until the edges are crispy. (Cooking time may vary, depending on the size of the potatoes.)
Let the potatoes rest for about 5 minutes before serving.
Top with parsley for garnish. Salt to taste.