To make sauce, place all ingredients in a saucepan over medium heat. Let simmer for about 15 minutes or until sauce thickens, stirring occasionally. Set aside.
Preheat oven to 450 degrees. Line a baking sheet with parchment paper and set aside.
Mix together arrowroot flour, garlic powder, chili powder, salt and pepper in a mixing bowl. Slowly whisk in milk ( batter will start out lumpy, but will end up thick and smooth) until mixture is lump-free and smooth.
Place florets in a large bowl and pour batter on top. Mix thoroughly, until each floret is coated well. Place florets on baking sheet and shake off excess batter. Bake for 20 minutes.
Take out of oven, let cool for 5 minutes. Place florets in a large bowl and add 3/4 of sauce. Coat each floret evenly in sauce and place back on parchment paper. Bake for another 10 minutes.
Heat oven to broil and brush remaining sauce on each floret and place in oven for 2-3 minutes (making sure florets don't burn).
Let cool and enjoy!