1. Combine the milk with the vinegar (or lemon juice) in a small bowl and set aside at room temperature.
2. Place the flour,sugar,baking powder,salt,pepper,rosemary and garlic powder in a food processor and process for a few seconds to combine. Add the butter and pulse until the mix is the consistency of breadcrumbs. Dribble in the milk and vinegar mix and continue to pulse until it forms a dough. (You could also make this by hand:rub the pieces of butter into the flour mix,then add the milk and vinegar and mix to form a dough.)
3. Tip out onto the kitchen bench and knead for a few seconds until smooth. Divide into three balls (they don't need to be exactly the same weight) and wrap loosely in cling film,then press to form three flattened discs. Refrigerate for at least one hour (or up to 2 days).
4. Preheat oven to 200C (180C fan-forced).
5. Line two or three baking trays with baking paper and set aside. Combine the seeds and salt in a small bowl and set aside. Lightly dust the kitchen bench with flour and roll out one of the pieces of cold dough as thinly as possible. Carefully roll up the dough with the rolling pin and unroll it onto the lined baking tray.
6. Sprinkle the seeds generously over the entire surface,pressing them in so they stick to the dough. Bake in the preheated oven for 18 to 20 minutes,or until light golden brown. Repeat with the remaining two pieces of dough.
7. Cool the crackers completely before serving. I like to place the large sheets of crackers straight onto the table,allowing guests to break off shards for themselves. The crackers keep well for up to 7 days in an airtight container.