Preheat the oven to 350°F (175°C). Line an 8x8-inch square pan with parchment paper, leaving overhang on all sides, and spray with nonstick spray.

Remove 8-9 pineapple rings from the can and pat dry with paper towels. Measure out 1/2 cup of pineapple juice for the batter and reserve remaining rings and juice for another use.

Pat maraschino cherries dry with paper towels to remove excess moisture.

Arrange pineapple rings evenly in the bottom of the pan, trimming as necessary to fit. Add cherries around or within the pineapple rings in a decorative pattern. Sprinkle with 1 1/2 tablespoons of brown sugar.

In a large bowl, whisk melted butter, white sugar, and 1/4 cup brown sugar until thoroughly combined. Add pineapple juice, lemon juice, and vanilla extract. Stir until mixture looks curdled.

Add flour, salt, baking soda, cinnamon, and nutmeg to the wet mixture and whisk until smooth.

Place dollops of batter over the prepared pineapple and cherries, gently spreading into an even layer with a spatula.

Bake in the oven until edges are golden brown and the center is set, 30-35 minutes. A toothpick inserted near the center should come out clean.

Cool bars in the pan for 15 minutes, then invert onto a plate or platter and remove parchment paper. Allow to cool completely.