Preheat oven to 350 degrees F. Spray the donut pan with cooking spray. Set aside.
In a bowl, whisk the flour, baking powder, baking soda, salt. Set aside. In another bowl, mix egg, brown sugar, milk, butter, vanilla, and guava marmalade until well combined. Add to the dry ingredients and mix. The batter will be very thick.
Scoop the batter into a ziplock plastic bag or piping bag, cut a hole in one corner, and pipe the batter into the donut molds, filling about 3/4 full.
Bake for 10 to 12 minutes, or until a toothpick inserted into the center comes out clean. Let cool for 5 minutes before flipping the pans upside down over a rack to remove the donuts.
Guava Mimosa Glaze
In a bowl, whisk powdered sugar, champagne, and guava marmalade together until completely smooth. Dip each cooled donut into the glaze and let the icing set until slightly hardened. Serve and enjoy!