From: The Sisters' Cafe
6 large potatoes, peeled
4-6 Tb half-and-half
1 tsp kosher salt
1 1/2 onions, finely chopped
6 Tb butter, divided
1/2 of a small head of cabbage, sliced thinly
1. Slice peeled potatoes in half and place in pot. Fill with enough water to cover and boil for 25 minutes, or until soft. While the potatoes are cooking, melt 4 Tb butter in large saucepan. Add minced onion and stir to coat with butter. Add cabbage over onions. Cover saucepan and cook over med-low to medium heat for 20 minutes, stirring occasionally, or until cabbage is soft.
2. Drain potatoes and add half-and-half (or milk) and salt. Mash with electric mixer. Stir together onion and cabbage mixture with mashed potatoes. Spoon into an oven safe dish and place under broiler until top is browned. Traditionally colcannon is served with a deep well in the center filled with melted butter... so I place 2 more Tb of butter on top and let it melt into colcannon.