Preheat oven to 375 degrees. Grease an 8x8 baking dish and line with parchment paper.
In a small bowl, beat egg and milk. Add oil and whisk until combined.
In a separate bowl, mix together dry ingredients. Add wet ingredients to dry and mix until well combined.
Pour half the batter into prepared baking dish and top with 1/3 of the crumble topping. Add remaining batter on top and sprinkle remaining crumble evenly on top. It won’t seem like a lot of batter, but I promise it will rise and get nice and fluffy during baking!
Bake for 30 minutes or until an inserted toothpick in the center comes out clean. Let cool on wire rack.
Combine glaze ingredients in a small bowl and drizzle over the top of the cooled cake. Cut into squares and enjoy!!