Place the mayonnaise into a bowl and add basil and chives. Season and chill covered for 2 or more hours.
Grease a baking dish. Preheat the oven to 180°C/350°F/Gas Mark 4. Heat oil in a pan and add garlic and red pepper and sauté for 3 minutes. Remove from heat.
Whisk the eggs in a bowl and stir in the cream, milk, flour, salt, chilli flakes and pepper. Ensure fully combined.
Pour this batter into the baking dish and sprinkle all the vegetables over the batter allowing them to sink. Scatter the chopped basil and crumbled feta cheese on top.
Bake for about 40 minutes till the batter is just set and starting to turn golden brown. Serve with a generous dollop of basil sour cream sauce.