Peel & cut potatoes into pieces. Boil in salted water until tender.

Drain and place in a bowl.

Add butter, horseradish, and milk. Mash by hand or with a mixer until combined.

Season with salt and freshly ground pepper.

Preheat the oven to 350F.

Line an 8-inch quiche dish or pie pan starting with bacon ends from the center.

A third of the bacon should hang over the edge of the pan.

Place every fourth strip offset towards the edge.

Spoon 2/3 of the mashed potatoes on top of the bacon.

Sprinkle half of the cheese over the potatoes.

Spread the remaining mashed potatoes on top leaving 3/4 inch around the edge.

Sprinkle the remaining cheese on the potatoes.

Pull the bacon slices hanging over the edge to the center of the tart.

Press down slightly so that the filling is completely covered.

Place the pan on a parchment-lined baking sheet.

Bake for 40 minutes.

Increase temperature to 400F and bake for another 25 minutes.

Remove from the oven. Gently lift the bacon layers with a utensil to check if all the bacon is cooked.

Place a large plate on top. Tilt sideways to drain off any excess fat into a heatproof container.

Cover with a serving plate and flip the pan over so that the bottom side of the tart is on top.

If the bacon isn't crispy enough on this side, return it to the oven and bake another 10-15 minutes.

Cut & serve.