Sweet and Sour Pork

1 lb. pork tenderloin, cut into 1/2 in. thick bite-sized pieces
2 1/2 Tbsp. balsamic vinegar, divided
kosher salt
2 tsp. low-sodium soy sauce
1 Tbsp. cornstarch
3 Tbsp. ketchup
3 Tbsp. sugar, plus a pinch
1/3 C. water
3 Tbsp. peanut or vegetable oil, divided
3 cloves garlic, pressed or finely minced
2 carrots, peeled and thinly sliced
3 scallions, cut into 1/2 in. pieces
3 C. snow peas, cut in half

Toss the pork with 1/2 Tbsp. vinegar and a pinch of salt in a bowl. Mix the remaining 2 Tbsp. vinegar, soy sauce, cornstarch, ketchup, 3 Tbsp. sugar, water and 1/2 tsp. salt in another bowl.
Heat 2 Tbsp. oil in a large skillet over high heat. Add the pork and slowly stir until it becomes mostly opaque, about 2 min. Remove the pork with a slotted spoon and transfer to a plate. Discard the oil and wipe out skillet.
Heat the remaining 1 Tbsp. oil in the skillet, then stir-fry the garlic with a pinch each of salt and sugar, 15 sec. Add the carrots and scallions and stir-fry until crisp-tender, 2 min. Add a little water if the garlic begins to stick. Add the pork, snow peas, and soy sauce mixture; stir until the pork is cooked through and the sauce is thickened, about 3 min.