Thaw puff pastry according to directions on package and halfway through thawing preheat oven to 400 degrees.: The kitchen will start smelling faintly of butter as the puff pastry relaxes and becomes pliable, and you want it cool but not frozen when cutting. This matters because a too cold sheet will crack when you try to shape it, while a too warm sheet will stick and tear. A common mistake is leaving it out until it becomes sticky, which causes tearing and uneven puffing. When it yields slightly to your touch but still feels cool, it is ready.
While puff pastry is thawing, in a small bowl and using a rubber spatula, mix together cream cheese, jam and food coloring while pressing mixture along bottom and sides of bowl to smooth large lumps.: As you press the cream cheese and jam together, you will feel the mixture loosen and a sweet, tangy aroma will emerge. That press and scrape action breaks up lumps and ensures a silky texture that spreads easily into the pastry without clumping. If you rush this step or skip smoothing, you can end up with pockets of unblended cheese that change the texture. Make sure you scrape the bowl so there are no hidden chunks.
Transfer to refrigerator until ready to use (so it's not runny, you can flash chill in freezer if you prepared this near the end of the pastry thawing).: Cooling the filling firms it and prevents seepage into the pastry, which helps the center stay creamy instead of puddly. You should feel the filling become noticeably firmer after a few minutes, and it will be easier to portion. A typical mistake is skipping chilling, which can lead to a soggy bottom and a filling that spreads too much. If you are in a hurry, flash chilling on a shallow tray for a couple of minutes works well.
Cut pastry into heart shapes using a 3-inch heart-shaped cookie cutter (space them as close together as possible so you can get as many as you can out of the sheet).: As you press the cutter, you will notice the clean edges of the dough and a slight resistance as the layers align. Close spacing maximizes yield, and the cut edges will show neat layers that bake into pronounced flakiness. If you squeeze or stretch the dough while cutting, the layers will compress and not puff as nicely. Aim for confident, straight downward cuts for even shapes.
Transfer hearts to a baking sheet lined with a silicone liner or parchment paper, spacing 1 1/2-inches apart.: Placing the cut shapes on parchment keeps them from sticking and makes cleanup easy, and the spacing gives the pastry room to expand into tall, airy layers. You should hear a faint rustle as you move them, and the sheets will look orderly and ready. Crowding them will cause the edges to bake joined and ruin the individual shapes, so keep them spaced as instructed.
Using a sharp pairing knife, lightly score a heart inside of each cut-out heart coming about 1/3-inch from the edge, without cutting entirely through bottom of the dough.: The scored line creates a decorative inner border and helps the center settle while the outer edge rises higher into crisp layers. You will feel a slight resistance as the knife scores the top layers only, and the visual cue is a faint line that does not separate the piece. Cutting through will make filling leak during baking, so be gentle and controlled with the blade.
Add 1 tsp of the cream cheese mixture to center of each heart then spread outward without covering the 1/3-inch edge.: The moment you set that spoonful down you will hear a soft plop and see a glossy mound that you will coax outward with a small offset spatula, leaving the border bare. This prevents the filling from burning and allows the edge to puff and brown separately. Overfilling or pushing the filling to the very edge makes it run and can create a soggy rim, so leave the margin intact.
Add strawberries over cream cheese layer, again without covering the edge. Using your fingertip brush the 1/3-inch edge with egg/water mixture.: Placing the diced strawberries should feel precise, and their fresh scent will brighten the filling. The egg wash brushed on the border creates a seal and a glossy finish as it bakes, and when it hits the oven it will smell faintly of baked egg and butter. If you drown the filling in fruit or miss the egg wash, the pastries will be pale or leak, so keep the fruit centered and the wash light but even.
Bake in preheated oven 14 - 15 minutes until edges are golden brown. Let cool on a wire rack then dust with powdered sugar. Serve the day they are prepared.: As they bake, you will hear a faint crackle and see the edges inflate and turn a deep golden color. The aroma will shift to a rich, toasty butter scent. Cooling on a rack prevents steam from making the bases soggy, and dusting with powdered sugar just before serving gives a delicate finish. A frequent error is leaving them on the baking sheet to cool, which traps steam and softens the bottom; transfer them promptly to the rack.
Serve the day they are prepared: Fresh pastries offer the best contrast of crisp edge and tender center, and the powdered sugar stays powdery only briefly before absorbing moisture. Serve warm or at room temperature for the best texture and flavor. Reheating can be done briefly in a low oven to refresh crispness, but prolonged storage will soften them significantly.