Step 1

Prep your ingredients: Cut cold butter into chunks then let them chill in the fridge at least 10 minutes. Combine flour and salt in a large bowl. In a large measuring cup, combine water, ice, and vinegar. Set aside until butter has chilled.

Step 2

Cut in the butter: Add the chilled butter cubes to the flour and toss to coat. Working quickly so the butter doesn't melt too much, squish the butter cubes between your fingers, rubbing the flour into the butter. The goal here is just to flatten all the cubes and break them into slightly smaller pieces. It's ok if there are still some big chunks. Try not to handle the butter too much or it will start to melt.

Step 3

Mix the dough: Splash about ¼ cup of the ice water into the flour and butter mixture. Use your hands or a bowl scraper to gently mix the flour and butter around until the water is absorbed. Drizzle another ¼ cup of ice water directly onto the dry bits in the bowl and repeat the mixing process. Continue adding water 1-2 TBSP at a time mixing until the dough holds together without crumbling when you squeeze it.The flour will have plenty of time to fully hydrate when the dough rests, so if you aren't sure, err on the side of a slightly drier dough.Dump the messy dough out onto a clean counter. Use a bench scraper to cut through the dough and redistribute the moisture if needed. Squeeze and pat the dough into a rectangle. Wrap in plastic wrap and let chill in the fridge for 1 hour.

Step 4

Do a double fold: On a clean surface lightly dusted with flour unwrap the chilled dough. Roll the dough into a long rectangle shape (I like to use a bench scraper to square it off as I go, but it doesn't have to be perfect). Move the rolling pin up and down but not side to side to keep the gluten strands moving in the same direction.Lift the dough occasionally to make sure it's not sticking; dust extra flour underneath if you need it.Dust any excess flour off the surface of the dough. Fold the top quarter of the dough down to the middle, fold the bottom quarter of the dough up to meet it. Then fold the top half down to hide the seam in the center. Rotate the dough 90 degrees.

Step 5

Do a single fold: Dust any excess flour off the surface of the dough. Roll the dough in another long rectangle, moving the rolling pin only up and down, not side to side. Fold the top third of the dough rectangle down. Then fold the bottom third up. Rotate the dough 90 degrees. Use your finger to make an indent in the bottom right corner of the dough so you know how to arrange the dough after it chills. Wrap the dough in plastic and chill for 30 minutes.

Step 6

Repeat: Remove the dough from the fridge. Arrange it so the corner with the indent is at the bottom right. Repeat the folding process — one double fold followed by one single fold. If you need to let the dough rest in the fridge for 30 minutes between each set of folds that's okay.

Step 7

After the final set of folds, wrap the dough tightly in plastic wrap and chill for several hours or overnight. It is now ready to be used and can be rolled in any direction.

Step 8

Combine drained tuna, mayo, red onion, celery, dill, paprika, salt, and pepper in the bowl of a mini food processor. Run the food processor on the puree setting until the mixture is very smooth and creamy.

Step 9

Add the shredded cheddar and tomatoes and pulse just a few times to combine — you want bigger pieces of cheese to give that "tuna melt" vibe. Adjust salt and pepper to taste. Chill until ready to use (it will stay good in the fridge up to a week).

Step 10

Remove chilled puff pastry dough from fridge. Divide in half. Wrap and refrigerate the dough you aren't using.Roll the puff pastry sheet to about ⅛" thickness. Use a bench scraper to square off the edges of the dough as you go, but it's ok if the edges are a little rough or misshapen. Trim the sheet to an 8x16" rectangle. Then divide the sheet in half so you have two 8x8" squares of puff pastry.

Step 11

Place one sheet on a lined sheet pan in the fridge to chill while you work with the other.

Step 12

Brush the egg wash along the outer edges of one 8x8" square of dough and through the center in both directions, creating a four section grid on the pastry. Spoon the chilled tuna filling into the center of each square, about 2 tablespoons each. Work quickly so the dough doesn't get too warm or sticky!

Step 13

Take the other 8x8" square of dough from the fridge and roll it slightly bigger in each direction. Gently drape it over the tuna melt filling. Start in the center of the dough and work outwards, pressing it down around the tuna filling, pushing out any air bubbles without squishing out any of the tuna. You should have about 1" of flat dough running around each of the tuna pockets.

Step 14

Use a pizza cutter to divide the square into quarters, separating the tuna hand pies. Crimp the edges of each tuna hand pie with a fork to seal them together. Trim away any excess dough around the edges.

Step 15

Place the four tuna hand pies on a silicone or parchment lined sheet pan and chill in the freezer for 30-40 minutes before baking. Repeat with the remaining dough and tuna filling.

Step 16

Preheat oven to 375°F while the hand pies are in the freezer. Right before baking, cut two slits in the surface of the pastry (be careful not to cut into the bottom sheet of dough!), brush the hand pies with an egg wash and top with flaky salt.

Step 17

Bake for 25-35 minutes until golden brown and flaky. Remove from the oven and let cool on a wire rack. Serve warm, room temp, or right out of the fridge. Store extras in an airtight container in the fridge for up to a week.