Gluten-Free Lemon-Poppy Seed Muffins

Preheat the oven to 350 degrees F (175 degrees C). Line two 12-cup muffin tins with paper liners.

Sift rice flour, tapioca flour, millet flour, arrowroot flour, guar gum, baking powder, baking soda, and salt together in a large bowl.

Combine lemon juice and zest in a 2-cup liquid measure. Add water to make 1 1/2 cups liquid; transfer to a large bowl. Add mayonnaise and blend with an electric mixer until creamy and most of the lumps are gone. Mix in sugar and poppy seeds. Pour into the flour mixture and beat for a full 2 minutes. Transfer batter into the prepared muffin cups.

Bake in the preheated oven until tops spring back when lightly pressed, about 15 minutes. Cool in the tins for 5 minutes. Transfer to a wire rack to cool completely.