Place the potatoes in a deep saucepan and cover with cold water to a depth of 2 inches.

Cook uncovered over high heat until the potatoes can be easily pierced with a knife, about 20 minutes.

While the potatoes cook, steam the broccoli and leek until the broccoli is very soft, about 15 minutes.

Drain in a colander. Drain the potatoes and place them in a deep bowl.

Using a sturdy fork, mash the potatoes into roughly 1-inch chunks. Add the broccoli and leek, mashing until only small lumps of the broccoli remain.

Add the milk, 2 tablespoons at a time, mashing until the texture is pleasing to you.

Season to taste with salt and pepper. In a small saucepan, melt the butter over medium heat until it is golden brown, 1 to 2 minutes, taking care it does not burn.

Stir in the mace. To serve, spoon the smashed potatoes into a serving bowl.

With the back of the spoon, smooth the top, leaving several shallow indentations.

Drizzle the butter, letting it pool in the hollows. Serve immediately.