In a pan or microwave, melt the butter. In a large bowl, mix together the butter and sugar. Add the vanilla extract, eggs, and oil, and whisk until smooth and light in colour. 

Sieve in the flour, cocoa powder and salt. Gently fold the mixture until it's fully incorporated, but be careful not to over mix.

Grease your Cast Iron Skillet Pan, then gently tip your brownie batter into the centre and spread evenly. You can also add any chopped nuts, peanut butter, chocolate chips, or fruit into the mixture at this stage. 

Fire up your Ooni pizza oven. Aim for 250˚C (482˚F) on the stone baking board inside. You can check the temperature inside your Ooni quickly and easily using the Ooni Infrared Thermometer.

Place your Skillet at the front of the oven and cook for about 10 minutes, making sure to turn regularly for an even bake. Check the consistency of your brownies by giving the pan a little shake. If it still wobbles in the centre then it’s not ready.

Once cooked, remove and let cool for a couple of minutes. Serve warm or cold, perfectly paired with a scoop of vanilla ice cream.