Step 1

Bring large pot of water to a boil. Fill large bowl with ice water. Add 1 tablespoon salt to boiling water; then, in 2 batches, cook green beans until just tender, 3 to 4 minutes.

Step 2

Using slotted spoon, transfer beans to ice water. Once cool, remove. Repeat with remaining beans.

Step 3

Meanwhile, in medium skillet, cook bacon on medium, stirring occasionally, until crisp, 8 to 10 minutes. With slotted spoon, transfer to paper-towel-lined plate.

Step 4

Pour off all but 2 tablespoons drippings. Add onion and cook, covered, stirring occasionally, until very tender, 8 to 10 minutes.

Step 5

Add vinegar and mustard and cook, scraping up any browned bits, until incorporated, 1 minute. Remove from heat and whisk in maple syrup and 2 tablespoons oil.

Step 6

When ready to serve, heat large Dutch oven on medium-high. Add remaining tablespoon oil and beans and cook, tossing, until heated through, 2 to 3 minutes. Remove from heat and toss with bacon vinaigrette and sprinkle with reserved bacon.