Preheat your oven to 180º Celsius Fan Force and line 2 large baking trays with baking paper. Set aside for now.
Pull out your 4 sheets of pastry and leave them on the bench to thaw out, I recommend covering with a clean tea towel to keep them from drying out.
In a large bowl pop the beef mince, onion, grated carrot, baby spinach, garlic, tomato paste, Worcestershire sauce, herbs and 1 egg. Combine thoroughly either using your hands or a large spoon.... Go on, get your hands in there!
Once combined you can pop that to the side for a minute and work on your pastry. By now it should be soft to touch and ready to be rolled out. Now this is critical to this pastry being a success. Used as is without rolling out/thinning out any further it will be a tough, gutless pastry, totally not what you want. Instead you need to roll it out to a fairly thin line using just a standard rolling pin.
Roll your pastry out on a piece of baking paper to stop it sticking to your bench. Once you have the pastry thin so that it is easily workable but not thin enough that you can see through it, you are ready. You'll need to have a pastry brush handy, a fork too for pricking and your last egg beaten in a small bowl.
Now break your mince mixture into 1/4 and either using your hands or a spoon place a thick line of it down the center of your pastry being sure to take it right to either end.
Using a pastry brush run a line of egg wash along the outer edges of your pastry and then fold one side over the other across the meat. Use the fork, dipped in a little egg wash, to gently push the top edge of pastry into the other to create a seal. Flip your long sausage roll over and prick your fork along the top several times to allow heat to escape during cooking.
Add extra beaten egg to the tops of the sausage rolls to help brown them up. Sprinkle generously with sesame seeds. Now you can cut your rolls as big or as little as you like, just remember that the larger they are the longer they will take to cook. I like to cut each roll into 6 pieces. Pop them straight onto your prepared tray and repeat the process with your remaining sheets of pastry.
Place your rolls relatively close together on the tray as they shouldn't spread much, just puff up slightly. Place them straight into a hot oven for 25- 30 minutes (rotating the tray once for a nice even golden brown) or you can even cover with cling wrap and refrigerate if needed for later in the day.