Add spelt, buckwheat, and salt into a large bowl and whisk with a fork until mixed.
Take butter out of the freezer and grate it. Cut butter into the flour with a fork or a pastry cutter until everything is very fine and incorporated (see 1st video above).
Cut in rendered pork fat.
Add water all at once and mix until it forms a dough.
Separate dough into two balls.
Flour balls and set on plastic wrap or inside a ziplock bag.
Roll out to 8 inch disks.
Place in fridge for about ½ hour.
Remove from fridge, let rest for a couple of minutes, and continue rolling on a floured surface until it is the size of your dish.
Place in pie dish, trim excess, tuck edge underneath, and decorate the edge with your fingers or a fork.
Notes
In Slovenia, butter comes in 250 gram blocks. Your best bet is to weigh it, but if you don't have a scale, a quick google search shows it's about 2 sticks butter + 1 and ¾ tablespoons in the states.