Preheat the oven to 350F. Grease a 9-inch springform pan with olive oil and line with parchment. Alternatively you can bake this brownie style in a greased 8x8 or 9x9-inch baking dish (olive oil brownies!).
Fill a medium pot with an inch or so of water. Bring to a simmer then reduce the heat to low and place a medium-large heat-safe bowl over top (it should be sitting above the water. Add your chocolate and let it slowly melt, stirring every minute, until melted. Remove the bowl from the pot and whisk in the olive oil and lemon zest (if using). Whisk in the yolks one at a time. Whisk in the almond flour and salt. Set aside.
In a separate medium bowl, add the egg whites and beat them until they firm up but haven’t formed stiff peaks, about 1-2 minutes
Slowly sprinkle in the sugar while continuing to beat the eggs. Keep beating until egg whites form stiff peaks, about 2-3 minutes.
Carefully fold ⅓ of meringue into the chocolate base, being careful not to deflate the egg whites (see video). Then carefully fold in the rest, making sure to mix in all of the chocolate at the bottom of the bowl until it’s a uniform batter.
Pour into the prepared pan and bake for 25-30 minutes or until the center is set and a toothpick in the middle is clean.
Let it cool in the pan for 10 minutes, then release the springform pan and transfer to a cooling rack to cool for at least 2 hours (if using a baking dish, just leave it in the dish). I find this cake is best served at room temperature.
Serve with whipped cream and your desired toppings.