Preheat the oven to 350°F (190°C). Line a muffin pan with paper liners or grease lightly. In a large bowl, whisk together flour, sugar, baking powder, baking soda, and salt.
In another bowl, whisk the sourdough discard, melted butter, eggs, sour cream, olive oil, milk, vanilla, lemon zest, and lemon juice until smooth.
Pour the dry ingredients into the wet mixture and gently fold until just combined—do not overmix.
Fold in the flour-coated blueberries.
Divide batter evenly into muffin tin (about ¾ full). Bake 18–22 minutes, until a toothpick inserted in the center comes out clean.
Let muffins cool for 10 minutes on a wire rack.
Stir together lemon juice and powdered sugar to make the glaze, then drizzle over muffins before serving.