Frangipane, a classic component of French baking, is a velvety, sweet, filling made of butter, eggs, sugar, almond flour, a bit of all-purpose flour, and a hint of almond extract that gets stirred together into a golden spreadable paste. This smooth nutty cream adds delicious richness and texture when swirled into the almond-scented cake batter, giving an exquisite nutty flavor and tenderness to the crumb. Studded with blueberries and scattered with sliced almonds, this summery loaf is simple yet stunning.