Beat first 6 ingredients at medium speed with an electric mixer until well blended. Spread about 1/2 cup cheese mixture onto each of 4 tortillas, leaving a 1/2-inch border. Top with remaining tortillas.
Heat a lightly greased large nonstick skillet over medium-high heat just until hot. Cook quesadillas in 4 batches, 1 minute on each side or until filling melts and outside browns. Cut into wedges, and serve with desired toppings. Garnish, if desired.