Make the cake:

• Preheat and prepare pan. Preheat oven to 350°F (180°C). Grease and flour a 8x8 inch pan (or 9x9 inch pan). Set aside.
• Make the topping. Whisk together brown sugar, granulated sugar, cinnamon, and salt in medium bowl until evenly combined. Add melted butter, with a wooden spoon or spatula, and stir to blend. Add the flour and toss with fork until moist clumps form. Do not overmix. You want soft, crumbles, and not a wet paste. Set aside. ½ cup (107 g) packed light brown sugar ¼ cup (50 g) granulated sugar 1 teaspoon ground cinnamon ¼ teaspoon salt ½ cup (1 stick, 113 g) unsalted butter 1 ¼ cups (150 g) all purpose flour
• Combine dry ingredients. In a medium mixing bowl, whisk together the flour, baking powder, and salt. 1 ½ cups + 2 Tablespoons (195 g) all purpose flour 1 ½ teaspoons baking powder ½ teaspoon salt
• Cream butter oil and sugar. In a second large bowl with an electric mixer on medium speed, cream butter, oil and sugar together until smooth and combined about 2 to 3 minutes. ¼ cup (½ stick, 57 g) unsalted butter ¼ cup (60 mL) neutral-tasting oil 1 cups (200 g) granulated white sugar
• Add eggs, vanilla. Add the eggs one at a time, beating well after each addition. Scrape down the sides and bottom of the bowl after each addition. Add vanilla extract. Beat to combine. 2 large eggs 2 teaspoons vanilla extract
• Alternate dry ingredients with sour cream. Alternate adding the flour mixture with the sour cream, beginning and ending with the flour mixture. ¾ cup (180 g) sour cream
• Bake. Add the batter to the prepared pan. Crumble the topping evenly over the top of the cake batter breaking it up into small clumps. Bake for 40-45 minutes until the cake is done when it's golden brown around the edges and toothpick inserted into the center comes out clean. Remove cake from the oven and allow it to cool before serving.