Directions

1. In the bowl of a stand mixer fitted with a paddle attachment, beat 1/2 cup room temperature butter and sugar together until fluffy, about 3 minutes, then add 1/2 teaspoon salt and 1 cup flour and beat until dough comes together. Chill for 30 minutes.
   
2. Spray a 8-by-8-inch baking pan with cooking spray. Adjust oven rack to middle position and preheat oven to 350°F.
   
3. Press dough evenly into prepared pan. Add a bit of flour to the dough or your hands to help flatten the sticky dough, as needed. Cover dough with slices of guava paste.
   
4. In the bowl of a food processor, combine oats, 1/4 cup cold butter, 1/4 teaspoon salt, and 1/4 cup brown sugar. Pulse 10 times. Add 1/2 cup flour and pulse until mixture resembles wet sand with some bigger chunks of crumble throughout. Sprinkle evenly over guava slices.
   
5. Bake until top is golden, about 40 to 45 minutes. Let cool completely. Cut the bars into squares and serve. These bars will last several days at room temperature in an airtight container.