Place a medium skillet over medium-low heat. Coat the bottom with a thin layer of olive oil. Add the onions and cook, stirring often, until deeply caramelized and meltingly tender, 45 minutes to 1 hour. Add the tomato puree and cook until reduced to a thick paste, 2 to 3 minutes. Add salt to taste and set aside.
Place a 12-inch paella pan or cast-iron skillet over medium heat. Coat the bottom with a thin layer of olive oil and then add the chorizo and garlic. Cook, stirring constantly, until the chorizo begins to render its fat and the garlic is soft but not too brown, about 3 to 4 minutes. Add the onion mixture and cook for 1 minute, stirring. Add the white wine to deglaze; reduce the liquid by half. Stir in the white beans and make a well in the center of the mixture, then add the clams, spooning beans over them to cover (this creates a pocket of heat that will help the clams cook). Cook until the clams open and the wine is reduced to a flavorful sauce that thickly coats the beans.
Remove from the heat and allow to rest for a few minutes before digging in.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Tournant, Portland, OR