Place mustard seed, fennel, coriander,
cumin, and peppercorns in a dry skillet.
Place over medium heat, moving skillet to
keep seeds from burning, until aromatic,
about 2 minutes. Mustard seeds will begin
to pop. Transfer seeds to a spice grinder,
cool slightly, and pulse until finely chopped
but not powdery. Transfer mixture to a small
bowl, and stir in the thyme, dry mustard,
ginger, 1 teaspoon salt, and sugar. Set aside.
Heat oven to 450 degrees. Position two racks in
oven. Spray a small roasting pan and a large
cookie sheet with cooking spray; set aside.
Cut potatoes into 1/3-inch-thick sticks. In a
bowl, toss with oil and 3 tablespoons spice
mixture. Spread in a single layer on cookie
sheet; bake on bottom rack 15 minutes.
Meanwhile, rub pork with 1 tablespoon
Dijon mustard. Sprinkle with 1/2 teaspoon
salt and 2 tablespoons spice mixture; pat
with hands to make it stick. Lower oven to
425 degrees; place pork in prepared pan. Place on
upper rack in oven. Cook until fries are
golden and pork is cooked through (145 degrees internally), about 25 minutes. Transfer fries to a bowl and pork to a cutting board;
cover both loosely with foil to keep warm.
Place roasting pan on stove over medium-high
heat; stir in wine, scraping bottom
of pan to release browned bits. Stir in stock;
cook, stirring occasionally, until reduced
by half, 5 to 7 minutes. Whisk together flour
with 1/4 cup water in a bowl; whisk into
simmering stock mixture. Whisk in remaining
tablespoon Dijon mustard; cook until
mixture begins to thicken, 2 to 3 minutes
more. Stir in berries; cook until they begin
to soften, about 2 minutes. Season fries
with remaining 1/2 teaspoon salt. Slice
pork, and transfer to platter. Serve immediately
with blackberry-mustard sauce
and chopped thyme.