1Preheat the oven to 350F. In a large bowl, beat the butter, oil and sugar for 1-2 minutes, until fluffy; beat in the eggs and vanilla.
2In a small bowl, stir together the flour, baking powder and salt. Add about a third of it to the butter mixture and stir by hand or on low speed with the mixer just until blended. Add half the buttermilk or yogurt, another third of the flour, the rest of the buttermilk and the rest of the flour. Stir just until blended, and spread into a 9"x9" pan that has been buttered or sprayed with nonstick spray. Spread the berries overtop.
3In a small bowl, blend the butter, oil, flour, sugars and salt and mix with a fork or rub between your fingers until evenly combined and crumbly. Sprinkle over the berries, squeezing the mixture in your hands as you go to create bigger chunks of crumble.
4Bake for about an hour, until golden and springy to the touch.