Preheat oven to 425ºF. Place the first four ingredients in the bowl of a processor* and pulse a few times to mix. Add the frozen butter and run for one minute or so until butter is incorporated. Add the mint and pulse again to mix. Beat the eggs in a small bowl, setting aside about one tablespoon for glazing before adding the cream. With the processor running, pour the liquid ingredients into the dry ingredients through the chute. As soon as the liquid is in, turn off the processor, pulsing once or twice to finish blending. Dough should not form a ball. Do not over-mix. (If you prefer to do this by hand, sift the dry ingredients together and cut in the butter. Mix in the mint. Add the prepared liquid (as above) and mix quickly, using just a few strokes. Avoid over-mixing.) Drop mixture onto a lightly floured surface, gather the dough, and pat into an eight-inch circle. Cut into eight wedges and place on an ungreased cookie sheet. Brush each scone with the reserved egg and sprinkle with sugar. Bake for about 15 minutes until golden brown. Serve while still warm with butter and jam.