Place a rimmed baking sheet on the lowest rack of your oven, and preheat oven to 300°F.
Mix together the melted butter and crushed graham crackers. Then, press them firmly into the bottom of a spring form pan.
Cream 3 blocks of cream cheese with ¼ cup of sugar. Stream in the condensed milk, mixing until smooth. With the mixer running, add eggs one at a time into the cream cheese mixture. Add in the lemon juice and zest, almond extract, poppyseeds, and yellow food color (if using). Mix slowly until incorporated.
Pour the filling over the graham cracker crust. Firmly tap* the pan against the counter (like you're dropping it on the counter at a height of one or two inches) to bring the air bubbles to the surface. You might use a toothpick to pop stubborn bubbles.
Place the cheesecake on the top rack of the oven. Pour a cup of room temperature water into the rimmed baking sheet on the lower rack. Promptly shut the oven.
Bake for 75 minutes at 300°F. Turn off the heat and leave the cheesecake in the oven for an additional 2 hours. Remove and chill in the fridge for 2 hours.
To serve, run a paring knife under hot water and carefully trace the knife between the crust and the springform pan. Gently unlatch the pan and remove the base from the sides. Clean the knife, and run under hot water again to cut cake into slices.
Make the Lemon Curd
Add the sugar to a small saucepan. Zest both lemons directly into the sugar. Juice both lemons into the sugar as well. Add in the eggs, and whisk until homogenous.
Turn the heat on to medium-low, and whisk for 6 minutes. Add in the cubed butter as you whisk, allowing each pat to melt in and emulsify. At around the 6 minute mark, the lemon curd should be notably thicker.
Pour at least ⅓ cup of the curd into the center of your cheesecake and spread it out with an offset spatula. You may use more if you prefer.
Store the leftovers but pouring into a container and pressing cling film down onto the surface of the curd. Refrigerate for up to a week. Great with scones!
Make the Almond Buttercream
Whip the butter for a minute to break it up and add air.
Slowly, one spoonful at a time, beat in the powdered sugar. Once all incorporated, it will look too dry. Add in the milk and almond extract. Whip until fluffy but able to hold its shape.
Transfer to a piping bag fitted with your favorite star tip.
Pipe generously around the edge of your cheesecake and, if desired, a fluffy mound in the center. Decorate with poppyseeds as desired.
Notes
*By "firmly tap," I mean it should make a good loud bang. You really want to force those air bubbles to the surface. Do this repeatedly, a good 10 to 15 times to makes sure the majority of the bubbles rise and pop.