Preheat the oven to 400 F (204 C). Line a 12 ct. muffin pan with cupcake liners. Make the spiced streusel by whisking the sugar and flour together in a large bowl until well combined. Work in the cold, cubed butter until well combined in the texture of wet sand.
Make the banana coffee cake muffins by whisking the flours, baking powder, baking soda, espresso powder and salt together in a medium sized mixing bowl until well combined.
In a larger mixing bowl, whisk the mashed banana, butter, sugar, eggs, sour cream and vanilla extract together until smooth and well combined. The liquid will be a pale yellow. Stir in the dry ingredients with a spoon until just combined.
Scoop the muffin batter into each lined muffin liner about halfway. Add in 1 teaspoon filling into each half filled muffin tin. Top each muffin tin with the remaining batter. Top with streusel.
Bake at 400 F (204C) for 10 minutes. Reduce the oven temperature to 350 F (177C) for the remaining time. Cool the muffins in the pan on a cooling rack for 25 minutes.
Make the espresso glaze by whisking the freshly brewed espresso or strong coffee and vanilla extract with the powdered sugar. Drizzle the espresso glaze on top of each muffin and enjoy!