In a large bowl, combine all of your dry pastry ingredients.
Next chop your butter into small chunks (roughly chopped, doesn’t have to perfect) and stir until the butter is coated with flour but still visible. (again doesn’t have to be perfect).
Add your cold water. Mix with a spoon until a rough dough forms.￼￼
Press the dough into a rough ball shape, wrap it in Saran Wrap and place in the fridge for 30min.￼
Next unwrap your dough and roll it out flat between two sheets of parchment paper. (Flour your parchment and rolling pin lightly with vital wheat gluten, repeat this whenever needed).￼
Fold each side of the dough inward (see photo), then turn the dough 90* and roll it out flat, squishing down the folded layers you just made. Then once again, fold each side inwards, turn 90* and roll it out flat. You want to repeat this 4-5 times to ensure layers of butter are spread throughout the dough. It will start off very rough looking but don’t worry about that! Just push the rough edges in a bit and continue repeating the process until it looks more uniform. ( If at any time your dough feels warm, place it back in the fridge or freezer for a bit to get cold again. You don’t want your butter to melt).￼￼￼￼
After you’ve rolled the dough out 4-5 times following step 7, fold it once more, Saran Wrap it and place it back in the fridge for another 30min.￼
Pre-heat your oven to 400*F.
Slice your chilled dough in half and store half in the fridge while your work on the current half. Roll this piece of dough out between parchment or on a very well "floured" surface/ using parchment paper on top to also prevent sticking. Roll it thinly but thick enough that you can still lift it up. Cut 4 squares out of this dough using a sharp knife or pizza cutter. These don't have to be perfect, just do the best you can and re-roll out the scraps if you need to to form the last square. Place the finished squares on a parchment lined tray, spread mustard over the squares leaving a small 1 inch border around the edges.
Top the mustard layer with the cheese slices (break the cheese into pieces to best fit inside the square) and then the ham slices (again breaking up the ham to best fit the pastry) and then sprinkle with pepper, again leaving the border around the edges. Brush the edges with the egg wash (1 egg whisked with 1/2 tbsp water).
Roll out the second half of the dough the same way as the first and place those squares on top of each of the prepared squares (try and make sure to roll out the squares to match up with the shape of the first ones). Gently press the edges of the top and bottom of your ham and cheese pastries together, then use a fork to go around the edges and press them together once more.
Brush the pastry dough with egg wash then slice a couple of holes in the top of the pastry to allow air to escape.
Bake for ~25min or until the keto puff pastry is crispy and golden.
Cool slightly then serve warm with dijon mustard for dipping. Enjoy your Keto Puff Pastry Ham and Cheese Sandwiches!