Preheat your oven to 350°Fahrenheit. Grease and line an 8x8 square baking pan with parchment paper.
Make streusel: In a medium bowl, melt the butter and let cool slightly. Mix the granulated sugar, flour, ground cinnamon, and orange zest with the melted butter. Mix until a coarse crumb forms. Place this in the fridge while making the cake batter.
8 tbsp unsalted butter, 1 cup all-purpose flour spooned and leveled, ¾ cup granulated sugar, ½ tbsp Orange zest*, 1 ½ tsp cinnamon
In a small bowl, mix together the flour, salt, and baking powder.
2 cups all-purpose flour, 2 tsp baking powder, ½ tsp salt
In a separate large bowl with a handheld mixer, beat the softened butter and sugar together until well combined. Add the egg, egg yolk, vanilla extract, orange zest, and sour cream.
¼ cup unsalted butter, ¾ cup granulated sugar, 1 large egg, 1 egg yolk, ¼ cup sour cream, 2 tsp vanilla extract, 1 tbsp orange zest
Pour half of the dry ingredients into the wet ingredients, alternating once with the orange juice. Mix until just combined.
½ cup orange juice
Pour the cake batter into your prepared pan. Top with the crumbled orange streusel.
Bake in the preheated oven for 33-38 minutes, or until a toothpick inserted in the center of the cake comes out clean. Let the cake cool in the pan for 10-15 minutes before removing the warm cake to a wire rack to cool completely.
Once cooled, top with orange icing- in a small bowl whisk together the powdered sugar, orange zest, and milk until smooth. Drizzle the glaze over the cake, slice, and enjoy with a nice cup of coffee!
½ cup confec sugar, 2-3 tsp milk, 1 tsp orange zest