Preheat the oven to 350°F. Spray a 9-inch square baking dish with cooking oil.
Prepare the Cake Batter:
Mix together the flour, xanthan gum (if needed), baking powder, and salt in a medium bowl. Set it aside.
Cream together the shortening and granulated sugar in a large bowl, with a mixer on medium speed, for about 5 minutes, until a textured paste forms. Scrape down the sides of the mixing bowl as needed.
Add the egg replacer mixture, applesauce, coconut milk, and vanilla to the creamed sugar. Blend with a mixer on medium-low speed for 2 to 3 minutes.
Gradually add the flour mixture and blend on medium speed, about 2 minutes.
Pour the batter into the baking dish, spreading it to the sides of the pan.
Prepare the Streusel Topping:
In a large mixing bowl, combine the oat flour and brown sugar, using a pastry cutter or pastry fork.
Cut the shortening into tablespoon-sized pieces. Use the pastry cutter to work the shortening into the flour.
Crumble the streusel topping over the batter.
Bake at 350°F for 32 to 36 minutes.
Notes
Note that the shortening for the cake is used at room temperature, whereas the shortening for the topping is used cold. Plan to let just the 4 tablespoons sit out to soften and leave the remainder in the fridge until you need it for the streusel.
Recipe by Go Dairy Free at https://www.godairyfree.org/recipes/gluten-free-coffee-cake-streusel-topping