In a medium bowl, combine with a whisk or fork the flour, sugar, salt, cinnamon and 1 tablespoon grated orange zest.
In a microwave or small saucepan, melt the butter, let cool briefly and then add the vanilla and Grand Marnier.
Pour the melted butter mixture into the dry ingredients and stir with a fork until all the butter has been absorbed and you have a uniformly moistened crumb mixture.
Stir in the chopped pecans and set aside while you make the cake batter.
Cake Batter
In a medium bowl whisk together the flour, baking soda, baking powder, and salt.
In a large mixing bowl, cream the butter and sugar until light and fluffy.
Add the eggs one at a time, beating well after each addition.
Scrape down the bowl and then beat in the vanilla and sour cream.
Add the combined dry ingredients to the creamed butter mixture just until combined. Do not over mix.
Pour the batter into the prepared pan, spreading evenly.
Crumble the crumb mixture over the batter completely covering the batter evenly.
Bake for 35 to 40 minutes until a toothpick inserted near the center comes out clean.