Preheat the oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving an overhang on two sides.

Melt 2 tablespoons butter in a medium saucepan over medium heat. Add 2 cups finely diced apples, 3 tablespoons brown sugar, 1 teaspoon vanilla extract, 1 1/2 teaspoons chai spice blend, and 1 pinch salt. Cook for 5 to 7 minutes, stirring often, until the apples soften.

Stir together 1 tablespoon cornstarch and 1 tablespoon water. Add the slurry to the 2-cup apple mixture and cook for 1 minute, stirring, until thick and glossy. Remove from the heat and cool for 10 minutes.

For Version A, stir together 1/2 cup melted butter, 1/2 cup brown sugar, 1/4 cup granulated sugar, and 1 teaspoon vanilla extract. Add 1 cup all-purpose flour, 3/4 cup rolled oats, 1 1/2 teaspoons chai spice blend, and 1/4 teaspoon salt. Stir until crumbly.

For Version B, stir together 1/2 cup melted butter, 1/2 cup brown sugar, 2 tablespoons pure maple syrup or granulated sugar, and 1 teaspoon vanilla extract. Add 1 1/4 cups fine almond flour, 3/4 cup certified gluten-free rolled oats, 1 1/2 teaspoons chai spice blend, and 1/4 teaspoon salt. Stir until moist crumbles form.

Press two-thirds of the chosen crust mixture firmly into the prepared 8x8-inch pan. Spread all of the cooled 2-cup chai apple filling over the crust, then crumble the reserved one-third crust mixture evenly over the apples.

Bake at 350°F for 28 to 34 minutes, until the crumble is golden and the filling bubbles lightly at the edges. Cool completely in the 8x8-inch pan for at least 1 hour, then lift out by the parchment and cut into 9 bars.