Step 1

Preheat oven to 350F. Line an 8-inch square pan with aluminum foil and spray with cooking spray; set aside. Lining the pan helps with cleanup and is recommended.

Step 2

Crust and Crumble Topping - In a large, microwave-safe bowl melt the butter, about 1 minute on high power.

Step 3

Add the flour, oats, sugars, optional salt, and stir to combine. Mixture will be dry and sandy with some larger, well-formed crumble pieces.

Step 4

Set 1 heaping cup mixture aside to be sprinkled on later as crumble topping.

Step 5

Transfer remaining mixture to prepared pan, and using a spatula or your fingers, hard-pack the mixture to create an even, smooth, flat crust; set aside.

Step 6

Mango Layer - In a large mixing bowl (same one used for crust and crumble is okay), add all ingredients and toss to combine. If sugar hasn’t dissolved fully that’s okay because it liquifies while baking.

Step 7

Evenly distribute mango mixture over the crust.

Step 8

Evenly sprinkle with the reserved heaping 1 cup crumble topping mixture. Before sprinkling, I squeeze the mixture in my palm to encourage bigger crumble pieces to form.

Step 9

Bake for about 50 minutes, or until edges are set and center has just set. Crumble topping should appear set and very pale golden and the mango filling mixture may be bubbling along the edges. Bars may take longer than 50 to 55 minutes if the mangos are very juicy. Watch your bars, not the clock, when evaluating doneness.

Step 10

Place pan on a wire rack and allow bars to cool for at least 1 hour before slicing and serving. If you try to slice bars before they’ve cooled completely, they’ll be extremely messy and could fall apart. Bars will keep airtight at room temperature for up to 1 week, in the fridge for up to 10 days, or in the freezer for up to 6 months.