Position a rack in the center of the oven. Preheat the oven to 350°F (180℃).
Grease and parchment-line a 8x4 - inch loaf pan.
In a small bowl, stir together the flour, brown sugar and cinnamon. Cut in the butter with a pastry cutter or rub in using your fingertips. Refrigerate while you make the pumpkin cake. ¼ cup (50 g) packed light brown sugar ¼ cup (30 g) all purpose flour 1 teaspoon ground cinnamon 2 Tablespoons (28 g) unsalted butter
In a medium bowl, whisk together brown sugar, oil, vanilla, pumpkin, and milk. ⅓ cup (71 g) packed light brown sugar ¼ cup (60 ml) neutral oil ½ teaspoon vanilla extract ½ cup (114 g) pumpkin puree 3 tablespoons (45 ml) milk
Stir in the flour, baking powder, baking soda, salt and pumpkin pie spice. Do not over mix. 1 cup (120 g) all-purpose flour ¼ teaspoon baking powder ½ teaspoon baking soda ⅛ teaspoon salt 1 teaspoon pumpkin pie spice
Spread batter in the pan and crumble streusel on top.
Bake in the preheated oven for 33-37 minutes until a toothpick inserted comes out with a few moist crumbs. Remove from the oven. Allow to cool in the pan for 10 minutes. Remove from the pan and cool before icing.
In a small bowl whisk together powdered sugar, vanilla, milk and cinnamon. Drizzle over cooled cake. Slice and serve. ½ cup (57 g) confectioners' sugar 2 tablespoons milk ¼ teaspoon vanilla extract ¼ teaspoon ground cinnamon