In a mixing bowl whisk together flour, granulated sugar, brown sugar, cinnamon and salt, while using fingertips to break up an clumps of brown sugar. Pour in butter and fold with a spatula until evenly moistened. Stir in pecans. Set mixture aside.
For the cake:
Preheat oven to 350 degrees. Spray a 9 by 9-inch baking pan with non-stick cooking spray (or butter and line with two sheets of parchment and butter parchment if you want to be able to lift out entire cake).
In a mixing bowl whisk together flour, baking powder, baking soda, salt, cinnamon, ginger, nutmeg and cloves for 20 seconds, set aside.
In the bowl of an electric stand mixer blend together granulated sugar and brown sugar with fingertips to break up clumps. Fit mixer with the paddle attachment (I recommend using an attachment that constantly scrapes the bowl, if not stop mixer occasionally throughout entire mixing process and scrape down sides and bottom of bowl) add butter and vegetable oil to sugar mixture and blend to combined. Mix in eggs one at a time. Then mix in pumpkin puree, sour cream and vanilla. With mixer set on low speed slowly add in dry ingredients and mix just until nearly combined, then remove bowl and fold batter with a spatula to just until combined.
Pour batter into prepared baking dish and spread into an even layer. Sprinkle crumbs into very small crumbles evenly over batter. Bake in preheated oven until center is set (it should spring back when gently touched, rather then remain indented), about 40 - 45 minutes. Remove from oven and cool completely on a wire rack.
For the glaze:
In a small mixing bowl whisk together powdered sugar, half and half and vanilla until smooth. Add more half and half or powdered sugar to thin or thicken as needed. Pour mixture into a small resealable bag. Seal bag and cut a tiny tip from one corner then drizzle over cake. Allow glaze to set then cut cake into squares. Store cake in an airtight container.