Homemade Cheese Crackers

INGREDIENTS

• 3 tablespoons unsalted butter, cut into 1/2-inch cubes, plus additional for baking sheets
• 1 1/2 cups / 7 oz / 200g whole wheat pastry flour, plus more for the counter
• 1 teaspoon dry mustard powder
• 1 teaspoon fine grain sea salt
• 6 ounces / 170 g Cheddar cheese, grated
• 2 teaspoons white wine vinegar
• 1 ice cube
• seeds (optional)