Thoroughly dry the salmon skin with paper towels, especially the skin then season with salt and pepper. Sprinkle all over with the cornstarch including the skin, shaking off any excess.
Heat a large skillet over medium heat, add vegetable oil and heat until the oil is shiny.
Working in batches if needed, add the salmon to the pan skin-side down. Use a fish spatula to apply firm, even pressure to the fillets so the skin crisps evenly. Cook until the skin is crispy, about 3 to 4 minutes.
Flip and lower the heat to medium-low. Continue cooking until the fish is nearly opaque and just barely cooked through, about an additional 4 minutes. Remove to a plate and repeat with the remaining fillets if needed.
Return the pan to medium heat, add the fennel and sauté until tender, stirring occasionally, about 5 minutes. Remove from heat.
For the white wine beurre blanc:
Add olive oil to a small saucepan over medium heat then add the shallots and sauté, stirring frequently until the shallots are soft, about 3 minutes.
Turn the heat up to medium-high and add the white wine, lemon juice and peppercorns. Simmer until ¼ cup remains, about 8 minutes.
Reduce the heat to love, Whisk in the butter, one cube at a time, waiting until each cube has emulsified into the sauce before adding another. Turn off the heat and season with salt. Stain the sauce and set aside.
For serving:
Plate the fennel and top with the filets of salmon. Ladle the beurre blanc over the top and serve immediately.