Sweet Rhubarb and Sour Cream Coffee Cake with Warm Streusel (Easy 75-Min Recipe)

Ingredients

• 200 g brown sugar, packed
• 65 g all-purpose flour
• 1 tablespoon ground cinnamon
• 1/2 teaspoon freshly grated nutmeg
• 115 g cold unsalted butter, cubed
• 100 g chopped walnuts or pecans, optional
• 315 g all-purpose flour
• 1 teaspoon baking powder
• 1 teaspoon baking soda
• 1/2 teaspoon salt
• 225 g unsalted butter, softened
• 300 g granulated sugar
• 2 large eggs, room temperature
• 2 teaspoons pure vanilla extract
• 240 g full-fat sour cream
• 350 g fresh rhubarb, diced to 1.25 cm pieces