Mix flour, cocoa powder, salt, and sugar in a bowl, until completely combined

Beat eggs, oil, and vanilla essence on medium speed for about 1 minute, then pour mixture into dry ingredients, mix until just combined

Fold in chocolate chips and frozen rhubarb, do not overmixed

Bake brownies on preheated 350 F for 30-35 minutes, depending on your oven, on parchment lined rectangular pan

Cool, slice, and devour!