Turn on the oven at 360°F. Turn flax seeds into a coarse flour using a mixer, add 3 tablespoons of hot water and set aside.
Put whole wheat flour, bycarbonate and salt in a large bowl.
Mix apple sauce, agave syrup and mashed potato in a jug, along with the juice and zest of the lemon.
Pour the liquid ingredients on the dry ones, add the flax seeds with water and stir quickly with a spoon, just as long as you get an homogeneous batter.
Divide the batter into 8 muffin molds and bake for 15 minutes. Remove from the oven and let the sweet potato muffins cool down before serving.
Note
These healthy sweet potato muffins keep well for a couple of days at room temperature, in an airtight container or in a glass jar and up to 5 days in the fridge. They also freeze well.