Heat the oven to 350 degrees.
Add the apples to a baking dish and toss with maple syrup, vanilla, a pinch of salt, 1/2 tsp cinnamon, and 1 tablespoon cornstarch
Melt Butter: Add butter to a small saucepan, increase the heat to medium, stirring often. The butter will bubble and sizzle around the edges once melted. Continue to stir. The butter will turn golden brown in around 5 minutes. Remove from the heat and keep it aside.
In a medium bowl combine the flour, oats, brown sugar, cinnamon, and salt. Add the melted butter and mix until well combined. Sprinkle this evenly over the apples.
Transfer this to the preheated oven and bake until the apples are tender and the crumb topping is deep golden brown. The crisp will be bubbling on the edges. It takes about 45 minutes.
Serve warm or at room temperature with vanilla ice cream.