I worked at a cafe over a decade ago that served this coffeecake. It is actually the only coffeecake I have ever had, but it is so good I don't feel the need to try any others.
Apple Cinnamon Coffeecake
4 cups flour
1 1/4 tsp salt
1 Tbsp cinnamon + 1/2 Tbsp
1 1/4 cup packed brown sugar
3/4 cup sugar
3/4 cup vegetable oil
1 1/2 tsp baking soda
1 1/2 tsp baking powder
1 1/2 cup buttermilk
2-3 medium Granny Smith apples
Preheat the oven to 325 degrees. Butter the inside of a 9 x 13" baking dish (like Pyrex). In a large bowl, stir together the flour, salt, 1 Tbsp cinnamon & sugars. Add vegetable oil and stir until combined. Measure out one cup of this mixture into a small bowl - this will be the crumble topping. Add baking soda and powder to the large bowl and mix well.
In a measuring cup, measure out the buttermilk and add the egg. Mix lightly with a fork. Add to the large bowl of dry ingredients and mix well until combined.
Peel & core the apples and slice in half. Slice each half in 1/8-1/4 inch slices. Stack these slices and cut in half. Add the apples to the batter and gently stir until well distributed.
For the crumble topping, take the 1 cup you removed earlier and mix in 1/2 Tbsp.
Pour batter into the prepared pan and sprinkle with the crumble topping. Bake for 50-70 minutes. Test the center with a bamboo skewer - it should come out moist but not wet.
Cool and serve with butter.