Key lime crumb cake 

Cook notes: You will need the juice of 15-20 key limes. You will use it in the cake batter and the key lime filling. You will need the zest of about 3 limes.
This cake does bake up fast, since the cake part is thin. Should be done at the 25 minute mark. You can use a cake tester to see if its done, although this could be hard as the cream cheese filling might get in the way. 
 Another way to see if it’s done is see if middle is jiggly.

¼ cup canola oil, plus more for pan
½ stick unsalted butter, melted.
2 ¼ cups all-purpose flour, plus more for pan
½ cup + 2 TB granulated white sugar
1 ts baking powder
½ ts coarse salt
1 large egg
½ cup + 1 TB half & half
3 ts key lime juice

Crumb Topping: (I wanted thick crumb topping so I doubled this part.)
1 cups flour
1 cups packed light brown sugar
¾ ts coarse salt
2 ts of lime zest (not key lime zest)
1 stick unsalted butter, melted & cooled

For the crumb topping:
In a medium bowl, combine all dry ingredients, pour melted butter over mixture, and toss with a rubber spatula until large crumbs form. Set aside.

Key lime filling:
8 ounces cream cheese, room temp.
1 large egg yolk
2-3 TB white sugar
1 TB fresh lime zest
1 TB key lime juice

For the cream cheese mixture:
Mix all in a bowl (really well) until ready to use.

For cake:
Place rack in center of oven, and heat oven to 350°.
Lightly butter a 9 x 13 baking pan and dust with flour, and tap to remove excess. (I’ve also used the Pam with Flour and it worked just fine); set aside.

In a medium bowl, sift together 2 ¼ cups flour, add in the granulated sugar, baking powder, and salt; set aside. In a second bowl, whisk together egg, butter, half & half, canola oil, and key lime juice (add this in at the very last minute to avoid curdling).
Using a rubber spatula, fold dry ingredients into egg mixture.

Spread batter evenly into prepared pan, and set aside. (to keep batter from sticking to your hand or spoon, just wet or oil your fingers or a spoon and spread evenly throughout pan).
The batter should be about half an inch or more high. It will cook/rise to an inch thick. (Don’t worry if the batter is very thin and hard to get into the corners, it does spread out as it’s baking).

Next put on the cream cheese mixture; I did this in vertical lines in the pan. You can make swirls if you want, just do not push down. Next add on the crumbs, do not push down. Then transfer pan to oven, and bake for 10 minutes, rotate pan. Then cook another 12-14 minutes or until a cake tester comes out clean. Using a serrated knife or bench scraper, cut into 3-inch squares. Store in an airtight container, in the fridge, for up to two days.