Preheat the oven to 350F. Butter a 9" round baking pan and sprinkle with sugar.
In a small bowl, mash together the butter, brown sugar and cinnamon. Dollop into the bottom of the cake pan.
Layer the apples into the bottom of the pan, being careful not to add too many as they will float to the top.
In a bowl, whisk the flour, sugar, salt, baking soda and baking powder.
In another bowl, whisk the olive oil, milk, eggs, orange zest, orange juice and Grand Marnier.
Add the dry ingredients to the wet ingredients and whisk until just combined.
Pour the batter into the prepared pan and bake for 1 hour, until the top is golden and a cake tester comes out clean.
Transfer the cake to a rack and let cool for 30 minutes.
Run a knife around the edge of the pan, invert the cake onto the rack and let cool completely.
Garnish with powdered sugar.
