In food processor, pulse cheese and jalapeno together until finely chopped. Add flour, mustard and pepper. Pulse just to combine. Add butter; pulse until mixture resembles coarse crumbs with butter the size of peas. Pour in 3 tablespoons (45mL) of ice water. Pulse just until dough starts to hold together, adding up to 1 tablespoon (15mL) more water if dough seems dry. Shape into disc. Cover with plastic wrap and chill until firm, 2 hours or for up to 24 hours. (Disc can be frozen for up to 2 months; thaw in fridge before rolling.)
Preheat oven to 375 degrees F (190 degrees C).
Transfer dough to lightly floured work surface. Roll dough to 1/4-inch (5mm) thickness, dusting with flour to prevent sticking. Using 2-inch (5cm) cookie cutter, cut out rounds. Transfer to parchment paper-lined cookie sheets.
Bake in centre of oven for 15 to 20 minutes or until golden. Cool in pan on rack for 5 minutes. Transfer to racks to cool completely.