Preheat oven to 350 degrees. Spray a lightly colored half sheet pan with nonstick cooking spray and set aside.
In a large bowl, whisk together oil, granulated sugar, brown sugar, eggs, pumpkin, yogurt, baking soda, cinnamon, nutmeg, salt and vanilla until mostly smooth. A few small lumps of brown sugar is fine.
Pour in flour and stir until just combined. Pour into prepared baking sheet and smooth the top as best as you can. Bake 15-20 minutes or until toothpick comes out clean after being inserted.
After cake has come out of the oven, make the glaze/icing: melt butter in a small saucepan over medium heat. As it continues to cook, it should start to foam, smell nutty and you should see little brown specks appear. Remove from heat.
Whisk in milk, powdered sugar, vanilla, cinnamon, nutmeg and nuts if desired. Pour hot icing over warm cake and spread to smooth the top.
Let cake come to room temperature or cool at least 30 minutes before cutting and serving. I mean, you can totally eat this hot, but I prefer it lukewarm or at room temp.