A warm slice of toast with a swipe of butter is one of life’s simplest pleasures. And it’s especially good when those components are a  homemade slice of bread  and high-quality butter. You may be thinking about blocks of pricey European-style butter from the grocery store, but that’s where homemade cultured butter steps in. All it takes is a quart of heavy cream, half a cup of yogurt, and a day or two for fermenting and chilling.  What is cultured butter?  Compared to regular butter, cultured butter is more flavorful due to fermentation. But while it’s fermented, it doesn’t taste funky. Rather, its butter flavor is deeper, richer, and nuttier.…