The flour toss is essential to keep blueberries from sinking. Use frozen berries straight from the bag (do not thaw). If using frozen, add 5-10 extra minutes to bake time. For dairy-free, substitute melted coconut oil or neutral oil. For gluten-free, use a 1:1 gluten-free flour blend and toss berries in it too. Store wrapped at room temp up to 3 days, fridge up to 5 days. Freezes well for up to 3 months; slice first for easy grab-and-go.