How to Make It
Combine milk and 1/2 cup unsalted butter in a small saucepan over medium. Cook, stirring occasionally, until butter is melted. Set aside.
Stir together cornmeal, greens, leek, and salt in a large heatproof bowl. Whisk in boiling water. Add warm milk-and-butter mixture. Whisk to combine.
Heat an ungreased cast-iron skillet or griddle over medium-high. Drop 1/4 cup of the batter, per cake, onto hot surface. Cook until lightly browned and crisp, 2 to 3 minutes. Flip, and cook other side until browned, 2 to 3 minutes. Serve hot with whipped butter.