For the Hollandaise, put the butter in a small sauce pan and set to low heat to melt it. Get a metal or glass bowl that will fit just inside a medium pot or saucepan without touching the bottom of the pot. Fill the medium pot with about an inch of water and set to a simmer over medium-low heat. In the bowl, whisk together the yolks and a squeeze of lemon juice until frothy. Place the bowl over the simmering water and start whisking the mixture. (You may need to use a dish towel to hold the bowl as it may get pretty warm.) When you start to notice the egg mixture slightly sticking to the sides of the bowl, whisk very quickly to incorporate air, to lightly cook the yolks, and to keep the yolks from curdling. After a minute or so, when the yolks are yellow and doubled in volume, remove the bowl from the heat.
Remove the melted butter from the heat and very, very slowly drizzle the butter into the yolks while quickly whisking to incorporate it (you may need a set of helping hands for this part). Keep whisking constantly so the yolks don't overcook. Once half of the butter has been added, add the butter more quickly, but be sure to not add the white milky solids that are in the bottom of the sauce pan. The mixture should be thick at this point (almost like mayonnaise), so add in the marinade to thin it out. Add a little water to thin out more, if needed. Season to taste with salt and pepper, then cover the bowl to keep the sauce warm. Optional: Make Hollandaise using a packet mix (like Knorr). Make according to package directions, adding the Stubb's marinade in place of 1/4 cup of the cream or milk.
To poach the eggs, fill a large sauté pan (with at least 2-inch high sides) or a large pot with at 1 1/2 to 2 inches of water and the vinegar. Set to medium heat; it should be hot enough so that small bubbles come up from the bottom constantly, but it shouldn't come to a heavy simmer or a boil. Crack the first egg into a small bowl, stir the water to make a gentle whirlpool, then gently drop the egg into the water. Help the egg stay intact by guiding it with a slotted spoon for a few seconds, then let it cook for 4-5 minutes, stirring the water occasionally. The white should be opaque and envelope the yolk, which should be slightly jiggly. Remove the egg with the slotted spoon and place on a paper towel lined plate. Depending on the width of the pan, you can cook 2-4 eggs at a time together, just make sure to space them about a minute apart.
To serve, toast the Texas toast slices, cut them in half, and place two halves on each plate. Top the toast with brisket slices, top each pile with a poached egg, then drizzle the Hollandaise on top of all of the eggs and serve immediately. If the Hollandaise needs to be warmed up, place it back over the pot of simmering water, stirring often, until warm.