Preheat the oven to 425F. Mix the Wet Mixture Ingredients together until homogeneous, may be a little lumpy but that is okay
Mix the Dry Ingredients together in a separate bowl, then mix in the wet mixture. Pour the batter into lined muffin tins, filling only up to ¾ of the muffin cavity
For the streusel topping, Mix together flour, sugar, oats and salt, then cut in the butter. Put the topping over the muffin batter and sprinkle on Demerara Sugar.
Bake at 425F for 5 minutes, then reduce temp to 350F and cook for an additional 17-20 minutes. After baking, remove the muffin tin from the oven and let cool for 10 minutes, then transfer the muffins to a wire rack to finish cooling.