In a medium saucepan, melt the butter over medium heat. Add the leeks and cook, stirring often until soft, about 10 minutes. Add the garlic and cook, stirring until fragrant, about 2 minutes. Whisk in flour and cook, stirring constantly, about 2 more minutes. Gradually whisk in milk, stirring constantly. Bring to a simmer, whisking constantly. Cook, whisking occasionally until thickened; remove from heat. Add cheddar; whisk until cheese is melted and mixture is smooth. Season to taste with kosher salt and freshly ground black pepper. Fold in asparagus (reserve tips), artichoke hearts, peas, chives, flat-leaf parsley, zest, cayenne pepper and half (2 ounces) of the fresh goat cheese.