Place a large bowl filled with ice water next to the stove. Bring 4 cups of water to a boil in a large saucepan; add the kale and return to a boil. Reduce the heat to maintain a simmer and cook for 3 minutes. Then drain, and plunge the kale into the ice water to stop the cooking. Drain again, and transfer to paper towels to dry.
Melt the 1 tablespoon butter in a large Dutch oven set over medium heat. Add the cabbage, onion, garlic, bay leaf, mace, white pepper, mustard, cayenne, and 1/2 teaspoon salt. Cook, stirring often, until the onions are soft, about 8 minutes.
Add the beer to deglaze the pan, and stir until evaporated, about 2 minutes. Add the chicken broth and reduce the heat to medium-low. Cook until the liquid is reduced by about half, about 5 minutes. Remove the bay leaf.
Stir in the blanched kale, and when it is warmed, remove the pot from the heat. Add salt and white pepper to taste. Cover and keep warm while preparing the potatoes.
Cover the quartered potatoes with cold water in a large pot. Place over high heat and bring to a boil. Salt the water generously, and then turn the heat down to a simmer and cook until the potatoes are tender, about 15 minutes. Drain the potatoes, setting the empty pot aside, and mash them in a large, sturdy bowl until they begin to have a creamy consistency.
Pour the cream into the empty potato pot, add the remaining stick of butter and a few pinches of salt, and warm over medium-low heat until melted. Combine the butter mixture with the potatoes and continue to mash until smooth.
To serve, divide the potatoes among bowls. Top each with some of the cabbage mixture and garnish with the bacon.