2 tbsp unsalted butter
1 medium leek, cut into thin rounds, well washed, and drained
1 lb spinach, trimmed, washed and drained
freshly ground black pepper
1/2 cup creme fraiche
3/4 tsp ground cardamom, or more to taste
Melt 1 tbsp butter in a large saute pan or skillet with a lid over low heat. Add leeks and season with 1/4 tsp salt. Cover tightly and gently sweat, stirring the leeks occasionally, until they are very soft, about 15 minutes. If the leeks begin to color at all, lower the heat and add a tbsp of water. Transfer to a plate and wipe out the pan.
Raise the heat to medium-high and swirl the remaining 1 tbsp butter in the pan. Add the spinach, starting with as much as will easily fit. Season with 1/4 tsp salt and a letter fresh pepper. Toss, adding remaining spinach as the first batch wilts down. Add 1/4 tsp salt and more pepper, and as soon as all of the spinach is completely wilted, remove from the stove and pour off any accumulated liquid.
Reduce the heat to low and return the leeks to the pan. Stir in creme fraiche and cardamom. Adjust the seasonings and cook for 1 minute.