1 cup vegetable oil
1 large onion, finely chopped
1 cup coarsely chopped celery
1 cup chopped celery, finely chopped
1 (10.75 ounce) can condensed cream of mushroom soup
2 tablespoons butter
2 eggs, beaten
1 teaspoon vanilla extract
2 cups all-purpose flour
2 teaspoons baking powder
1 teaspoon baking soda
1 teaspoon salt
1 teaspoon baking powder
1 teaspoon baking soda
1 cup yogurt
1 egg
1 cup milk
3/4 cup honey
Heat 1 cup vegetable oil in a large skillet or frying pan over medium heat. Saute onion until golden and tender; remove from skillet. Remove skillet and place in a separate large bowl.
In a large bowl, combine celery, onion, celery mixture, mushroom soup, butter, eggs, honey, and vanilla. Mix thoroughly. Stir in flour, baking powder, baking soda, salt, baking powder, baking soda, and yogurt. Mix thoroughly.
Mix flour mixture into remaining batter. Flatten with fingers; fold into cream of mushroom soup mixture, continuing to oat. Spread over mushroom squash mixture. Cover with cake. Let stand overnight before frosting. Cut into 1/2 inch squares. Store in refrigerator for 2 to 3 hours, stirring occasionally.