Mix your oil, egg and milk in a large mixing bowl, whisking them together.
In a small bowl combine your flour, sugar, baking powder and salt. Sift together or mix with a whisk.
Add your dry ingredients to your wet ingredients in 1/3rds, stirring well each time.
Pour into a greased 9x9" or 8x8" pan.
Melt 1 Tbsp butter in a 2 or 4 cup measuring cup.
Add the packed brown sugar, flour, cinnamon and chopped nuts to the measuring cup.
Stir and sprinkle on top of the cake. I find using my fingers to sprinkle works best because it wants to stick to itself.
Bake in a regular oven 375 degrees for 25 minutes. In my convection, air fryer toaster oven, I bake it 375 degrees for 17 minutes.