Grill the bacon gently to your liking and cut each slice into three.
Divide the mince into two. Shape into burger patties, season each side and quickly seal in a frying pan with oil on both sides (do not cook. This is to seal so they won’t dry out when baked). Remove from pan and allow to cool. On top of a patty, spoon a tbsp of the chutney and cover with half the bacon. Place a tbsp of the sliced gherkins carefully on top, add a touch of mustard, and then layer with cheese. Repeat with the remaining patty and rest in the fridge until needed.
Lay the pastry out, and using a bowl that's about double the size of your meat patty in diameter, cut two discs for each burger. Then cut two discs the same size as your meat patty. Remove the burger stacks from the fridge and over one of the stacks, carefully place the larger of the pastry discs over and smooth around the edges and sides (like icing a cake). Trim the bottom so the pastry just overlaps the burger. Brush the smaller disc with egg yolk and place over the base of the burger sealing the two pastry discs together. Repeat with other stack.
Rest in fridge for 15 mins until firm and cool pastry before cooking.
Place on non-stick baking tray (or covered in non-stick baking paper) and brush all over with egg yolk. Sprinkle sesame seeds over the top and bake for 20-25mins on 190c until golden brown.
Rest for 5 mins before eating.