Mix flour, baking powder, baking soda, and spices in a medium bowl. Beat butter and brown sugar until fluffy. Continue to beat, adding molasses, followed by the flax seed mixture, until smooth. Alternating three times, beat in dry ingredients and plant creamer to form a smooth batter. Pour batter into prepared pan and bake until firm, 35 to 40 minutes. Set on a wire rack for 5 minutes to cool. Invert onto the wire rack to completely cool. (Can be wrapped and stored at room temperature overnight.)