1
Preheat the oven to 350°F (180°C).
2
Line an 8-inch square baking pan with parchment paper.
3
Add the sugar and salt to the egg yolk and mix well.
4
Add the flour and mix well.
5
Add the unsalted butter and mix until a dough forms.
6
Add the lemon juice, lemon zest, and vanilla extract, and mix well.
7
Pour the batter into the prepared baking pan and smooth the top.
8
Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.
9
Let the brownies cool completely in the pan before cutting into squares and serving.