Bratwurst, Beer & Cheddar Pretzel Pot Pie



1 tablespoon olive oil
3 bratwurst sausages
4 slices bacon, chopped
1 large yellow onion, diced
3 garlic cloves, minced
2 medium carrots, diced
2 celery stalks, diced
1 pound crimini mushrooms, sliced
1 teaspoon salt
1/2 teaspoon black pepper
1/2 teaspoon crushed dried red pepper
2 teaspoons chopped fresh thyme
1/4 cup all-purpose flour
1 tablespoon grainy mustard
1 cup beef (or chicken) stock
1 (12-ounce) bottle beer (Oktoberfest beer would be great!)
6 to 8 small red potatoes, diced
3/4 cup half and half
2 cups shredded sharp cheddar cheese
Homemade Pretzels (recipe follows) or Store-bought pie crust
1 large egg
1/4 cup pretzel salt or sesame seeds