Boil the potatoes - Place the diced potatoes in a large pot and cover them with water. Bring the water to a boil over high heat, then reduce the heat to medium-low and let the potatoes simmer until they're tender, about 10-12 minutes. Drain the potatoes in a colander, then return them to the pot. Be sure to keep an eye on the potatoes while they're cooking so they don't overcook and become mushy.

Mash the potatoes - Using a potato masher or fork, mash the potatoes until they're mostly smooth but still a bit chunky. Set aside. If you don't have a potato masher, you can use a fork or a hand mixer to mash the potatoes. Just be careful not to overmix, as you don't want the potatoes to become gluey.

Cook the vegetables - In a large skillet or frying pan, melt the butter over medium heat. Add the chopped onion and minced garlic and sauté for 2-3 minutes, until the onion is translucent and the garlic is fragrant. Add the cooked vegetables and stir to combine. Cook the vegetables for 5-7 minutes, until they're heated through and starting to brown. Make sure the vegetables are well-drained before adding them to the pan, as any excess water can make the Bubble and Squeak soggy.

Mix in the mashed potatoes - Add the mashed potatoes to the skillet and stir to combine with the vegetables. Use a spatula to press the mixture down into the pan and smooth out the top. Let the mixture cook for 5-7 minutes, until the bottom is golden brown and crispy. Don't be afraid to press the mixture down firmly into the pan - this will help it get crispy and golden brown.

Flip the Bubble and Squeak - Place a dinner plate upside down over the skillet and use oven mitts to carefully flip the skillet over so that the Bubble and Squeak is now on the plate. Slide the Bubble and Squeak back into the skillet, uncooked side down. Cook for another 5-7 minutes, until the other side is golden brown and crispy. If you're nervous about flipping the Bubble and Squeak, you can also use a spatula to flip it in sections. Just be careful not to break the mixture apart while flipping.

Serve and enjoy! - Once the Bubble and Squeak is golden brown and crispy on both sides, remove it from the skillet and slice into wedges. Serve hot, garnished with chopped fresh herbs and a dollop of sour cream or plain Greek yogurt, if desired. Bubble and Squeak is a great dish to customize based on your preferences. You can add in any leftover vegetables you have on hand, or even swap out the potatoes for sweet potatoes or butternut squash for a twist on the classic recipe.