Cut speck into 1cm cubes, and place into a cold saucepan to render its fat on medium-high, until golden-brown. Transfer to a bowl.

Cube chicken, coat it with the mustard, and sear it in the same saucepan. Transfer to bowl of speck.

Note: further cooking on chicken occurs in the following steps, don't fret if it's not fully cooked in this step.

Sauté onion in the same saucepan until translucent and fragrant. Add leeks, and cook until they're relaxed, and fragrant, stirring occasionally.

Add wine and stock, increase heat, and cook to reduce by half.

Return speck and chicken to saucepan, add garlic, cornflower, herbs, salt, and pepper. Stir to combine, cook for 5 minutes. Add peas, season to taste.

Remove from heat, and allow this filling to cool. If you're time-poor, place your filling into a baking tray, and place in your freezer for a quick temperature turn-around. Its best your filling is cooled, to ensure a perfectly crispy (not soggy) crust.

Once cooled, preheat your oven to 180°C, and place the filling evenly into a baking dish. Top with sheets of puff pastry, and make a small slit in the centre to allow air to escape while baking.

Brush pastry with whisked egg for a crisp, golden top, and finish it with an optional sprinkle of sesame seeds.

Bake for 30 minutes, or until the pastry is golden-brown.

Serve with a fresh and tangy leafy-green salad, and devour.