If you haven't already done so, melt the butter now so it can cool before you need it. Just pop it in a microwave safe bowl, heat for 10 second intervals and stir in between until completely melted.
Preheat the oven to 325°F/160°C.
Grease an 8-inch square pan with butter.
In a large bowl, stir together the cornmeal, flour, sugar, brown sugar, thyme, salt, baking powder and baking soda. Take out 1 tablespoon of flour mixture and set it aside.
In a small bowl, whisk together the eggs, buttermilk, vanilla and lemon zest.
Pour the buttermilk mixture and the melted butter into the dry ingredients.
Stir gently until everything is just incorporated.
In a small bowl, mix together the 1 tablespoon of set aside flour with ¾ cup of blueberries. This helps make sure the blueberries won't sink while baking.
Gently fold the ¾ cup of blueberries into your batter.
Pour the batter into your prepared pan.
Sprinkle the remaining ¼ cup of blueberries over the top of the batter.
Bake the cornbread for 40 minutes, or until the edges turn golden and a toothpick inserted into the center comes out clean.
Recipe by Cooking is Messy at https://www.cookingismessy.com/2015/10/29/blueberry-thyme-cornbread/