Preheat the oven to 180°C (350°F). Line a muffin tin with 12 paper liners.
In a medium mixing bowl, whisk together the plain flour, almond flour, baking powder, sea salt and granulated sugar. Set aside.
1 ¼ cups all-purpose flour, 1 cup almond flour, 2 teaspoons baking powder, ½ teaspoon fine sea salt, ½ cup granulated sugar
In a large mixing bowl, whisk together the sourdough discard, eggs and milk until smooth. Next, whisk in the oil, melted butter, vanilla and almond extract until well combined.
7 ounces sourdough discard, 2 medium eggs, ½ cup milk, ¼ cup vegetable oil, ¼ cup butter, 1 teaspoon vanilla extract, 1 teaspoon almond extract
Add the dry ingredients to the bowl with the wet ingredients and fold in using a wooden spoon until just combined. If you have some streaks of flour left behind that's good.
Gently fold in the blueberries. Divide the mixture between the muffin liners in your prepared tin. They should be almost but not quite full, top with a few additional blueberries and sprinkle over the Demerara sugar.
1 ½ cups blueberries, demerara sugar
Bake in the preheated oven for about 25 minutes until golden brown and an inserted cake tester comes out almost clean.
Leave to cool in the muffin tin for 5 minutes before transferring to a cooling rack to cool completely.