Preheat oven to 350°F/180°C.
Line the baking pan with parchment paper and spray with oil. Melt the chocolate and butter on low heat on the stove until smooth.
Transfer the chocolate to a large bowl, add vanilla, and mix well. Let it cool for a few minutes.
Stir in sugar, eggs, and salt. It is important to work quickly so that the eggs do not harden from the heat of the chocolate.
Add almond flour and mix until everything is combined.
Spread batter into the prepared pan and flatten the mixture with a spatula. The mixture will be very thick, and that is OK.
Bake for 25-30 minutes. Do not overbake- a toothpick stuck in the center comes out with moist chocolate crumbs.
Cool completely to room temperature. Dust with powdered sugar if desired.
Slice and enjoy!